EFFECT OF LIGHT ON LEAF INCLINATION OF

TRITICUM AESTIVUM

III. SeE詞lingAge and PhotQsensitive Region

Kazuyoshi KIMURA

As shown in the previous papers (Kimura 1974， 1975)， blue light promot田 bladeinclination of the first leaf in wheat plant， and the maximum inclination occurrs when the plants are ex卵白dto 1600 ergl cm2fsec or more of blue light at 20-250C for 48 hours. It was also shown that the inclination r白 ponsesdiffer greatly depending on the age of seedlings at the s同rtof blue light treatment. Maximum r田 ponsewas ob田 rved9 days after germination when the plants were grown in dark-ness a t 200 C.

In the present experiments， effect of blue light on blade inclination was examined in de同ilwith etiolated s田 dlingsat various ages. Further-more， some experiments were conducted to find photosensitive site of leaves.

MATERIAL AND METHODS

The material used was the seedling of Triticum aestivum，“Shirasagi Komugi ". Plants in plastic trays were grown on vermiculite at 20oC. The intensity of light used was about 2000 ergjcm2fsec at the plant level. Procedure of experimentation and light source were similar to th偲 edescribed in the previous paper (Kimura 1974).

RESULTS Seedling age 1) Age in days

In the pre田 ntexperiment， plants were grown in darkness at 200C for 6-12 days and subsequently expo民dto continuous blue light for 24 and 48 hours. Observations were made immediately after the light treatment.

Results shown in Fig. 1 indicate that the inclination responses to blue light differ greatly depending on the age of the民edling. In bOth 24-and 48-hour tr回 tments，inclination respon田 appearedin the 6-day-old seedlings and it increased to the maximum in 8-or 9-day-old seed-lings， older民 edlingsbeing less sensitive. Changes in photωensitivityas infiuenced by the seedling age， were greater in the experimental group in which blue light was given for 48 hours than in the group in which blue light was given for 24 hours. No significant r田 ponsewas observed when laminar joint was still enclosed in the coleoptile.

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Fig. 1. Effect of seedling age on inclination response in the first leaf of wheat plants. Plants were cultured in darkness at 20.C for 6-12 days， and then exposed to blue light for 24 and 48 hours. ー一一一:24-hour treatment. 一一一一ー一:48-hour treatment.

2) EfJect 01 removal 01 coleottile In the above-mentioned experiment， young seedlings whose laminar

joint of the first leav田 werestill in coleoptile failed to show the inclina-tion r白 ponse. In the present experiments， the e町ectof removal of coleoptile on the inclination r白 ponsewas investigated. Plants cultured in darkness at 200C for 3-10 days were divided into two groups， each containing the plants at various ages. One group was removed the coleoptile just before blue light treatment， while the other one was not. To prevent the falling of the blade and leaf-sh回 th，the apical parts of the leaf blade were cut 0百 byscissors， leaving 5 cm of the blade. After the plants were subjected to blue light for 48 hours， the inclination angles were measured. Results are shown in Fig. 2.

In the pr田 entexperiment， the laminar joint of the intact plants appeared above the top of the coleoptile on the 7th day after germina-tion. If the plants were deprived of coleoptile， the blade inclination was promoted by blue light to some extent， even in 3-to 6-day-old seedlings. Even in∞ntrol plants cultured in darkness， the inclination was slightly promoted by removal of the coleoptile. The inclination response加 bluelight showed the maximum value 9 days after germination in both intact and treated plants.

Effect of Light on Leaf Inc1ination of Triticum aestivum 137

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Fig. 2. Effect of removal of coleopti1e on leaf-blade inclination of wheat plants irradiated by blue light. Plants were cultured in darkness at 20.C for 3-10 days， and then the coleopti1e was removed. Immediately after cutting the coleopti1e at various ages， plants were exposed to blue light for 48 hours.

自一一一:Plants deprived of coleopti1e， 一一一一一一:Intact plants.

3) Seedling age and groωth tattern In the present expeIiment， relation between the seedling age which

affects the photosensitivity and the growth開 tternof the seedlings was examined. Plants were cultured under continuous irradiation of various colored ligh也 andtotal darkness at 20oC. Intensity of the lights was adjusted to 2000 ergfcm2fsec at the plant level. Every day during the experimental period， 10 plants were sampled at randam to examine the length of coleoptile， leaf sheath， leaf blade and blade angle of the first leaves. (Fig. 3).

Under any colored light， coleoptile elongation stop戸d1 dayafter germination， and then leaf blade elongated rapidly and attained almost its maximum length at 4-5th days. After the leaf blade attained almost its maximum length， leaf sheath began to elongate and nearly reached their maxima at 7-8th day. These growth pattern was similar in all colored lights tested. However， in total darkness， the elongation of coleoptile stopped 2-3 days after germination， and its final length was somewhat larger than those in colored lights.

The leaf sheath elongated rapidly in darkness during the 4th and 8th day after germination， and its final1ength which was attained on 8th day

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Eff，田tof Llght on Leaf Inc1i回tionof T，.iticum aostivum 139

was considerab1y 1arger than that in light. The 1aminar joint appeared from the top of co1eoptile on the 6th day after germination in b1ue， green， yellow and white ligh旬， and on the 7th day in red and darkness.

In all grou凶， 1eaf sh回 thwas stopped the ・e1ongation1-2 days after the ap開 aranceof the 1aminar joint. Leaf b1ade 加ganto inclinate when 1aminar joint appeared from the top of co1eoptile， and the maximum e1ongation of the b1ade occurred on 8-9th day when the 1eaf sh回 thstopped the e1ongation. The inclination ang1e incr，回sedgr四 t1yby b1ue light， but not much by gr，田n，yelIow， red and white light， as had bE封筒1

reported in the previous paper (Kimura 1974).

Photosensitive site

. The r，白u1tsof the experiments mentioned above sugg白 tthat the laminar joint is the photosensitive region in inclination respon記. The following experiments were designed to determine the phot偲 ensitiveregion of 1eaf in wheat p1ants which cuItured in darkness for 8 days.

1) Effect of removal of leaf blade To examine the ro1e of the 1eaf b1ade in the inclination r，白pon詑，

the apica1 pa吋sof the first 1eaf b1ade were cu t 0百bya sci田 ors，1eaving 0.5， 1 and 5 cm of the b1ade. Thereafter， the p1ants were subj配 tedto b1ue light for 48 hours， and the inclination response was∞m戸時dwith that of intact p1ants. As the contro1， p1ants deprived of the apica1 parts of the b1ade were kept in tota1 darkn回s. R田 u1tsare shown in Fig. 4.

No significant difference in blade inclination were found between the intact and treated plants. This sugg，邸包 that the 1eaf b1ade d偲 snot p1ay an important ro1e in the contro1 of b1ade inclination.

2) Shading of various regions 0/ leaf To obtain more detai!ed information on photosensitive region of

1eaf， the following experiments were conducted. After 1eaf b1ade， 1aminar joint or 1eaf sh伺 thwere painted by b1ack marker* to shade from the light， p1ants were subjected to b1ue light for 48 hours. Contro1 p1ants with b1ack marker on the回 meregions of 1eaves were grown in darkn回 S

to examine the e百'ectof b1ack marker itself. The inclination r回 pons白are shown in Fig. 5.

When the shading treatment was given to the 1eaf b1ade and/or 1eaf 油田th，1eaving 1aminar joint， the b1ade inclination was near1y the回 meas that of the plants without shading. If the 1aminar join也 wereshaded，

however， e町'ectof the light was gr回 t1ydiminished. As the b1ade incli-nation in darkness was not affected by black marker， it is considerちdthat the b1ack marker used in the pr白 entexperiment has no e圧配ton the blade inclination by itse1f.

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Eこここコ Blue light irradiation. 医a Darkness

In another experiment， laminar joint was covered with floss-silk dyed black to shade from blue light irradiation. Result of this experiment was similar to that shown in Fig. 5， though the data is not prl田entedin this paper.

From the results of these experiments， it is noticed that photosen-sitive region of leaf in inclination response is the laminar joint itself.

3) lrradiationωith narroωbeam. Effect of localized irradiation was examined by giving narrow beams

to different regions of the leaf. The s田dswere sown in 18 x 70 mm glass tubes containing vermiculite. The tubes with one seed in each wete immediately subjected to darkness at 200C for 8 days， and then the apical parts of the 2nd leaf blades were removed by cutting 5 mm below the joint of the 1st leaves. Then， plants were exposed to blue beam of 伺. 1000 ergfcm2fsec for 48 hours. In the preceding experiments， all

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Effect of Light on Leaf Inc1ination of Triticum aest;vum 141

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Fig. 5. Effect of shading given to various regions of leaves on leaf blade inclination of wheat plants irradiated with blue light. Plants were cultured in darkness at 20・C for 8 days， and then various parts of the fir百tleaves were painted by black marker. Immedi. ately after the treatments. plants were exp偶 edto blue light or kept in darkness at 200C for 48 hours.

E二二二コ Blue light irradiation. ~ Darkness

irradiations were given from the top. 1n the present experiments， how-ever， horizontal narrow beam was given through a slit of ca. 1 mm width， prepared on one side wall of the box (30 x 30 x 20 cm). Each region of leaves to be irradiated was placed at 3 mm distance from the sliL The width of the irradiated region on the 1回 veswas about 2 mm. R田 ultsare shown in Fig. 6.

Blue beam given to the laminar joint caused an increased inclination. The blue beam given to the leaf blade or sh回 thhad some e白 ct，but the effect was weak as compared with that of the beam given to the laminar joint.

Results also indicate the difference in sensitivity of the opposite side of the joint. Localized blue light given to the inner part of the joint 但 U鵠 ddeep inclination as compared with that given from the outer part.

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The pre田 ntexperiments had some technical di伍cultyin giving the light beam to the definite region throughout the irradiation period. The leaf sheath elongated during the irradiation period， and the position of laminar joint changed， while the beam was fixed. Nevertheless， these results suggest that the site of photo-perception is laminar joint.

4) Experiments with eXPlants Shading experiments were conducted with the excised first leav田.

Plants were cultured in darkness at 200C for 8 days， and the explants ∞nsisting of a laminar joint with 5 cm pieces of leaf blade and 5 cm piec田 ofleaf 油田thwere taken from the 1st lea ves. Thereafter， each part of the laminar joint was painted by black marker， as shown she-matically in Fig. 7， to examine the difference in sensitivity of回 chpart to blue light. As the control， non-shaded explants were exposed to blue light and darkness. The explants were inserted vertically through the

Effect of Light on Leaf Inclination of Triticum aestivum 143

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rneshes of a plastic net covered on petri dishes containing dist. water. After a 48-hour treatrnent with blue light of 2000 erg/cm2/sec， the incli-na tion respon田 swere examined.

The blade inclination occurred in the explants. too， but showed sorne-what smaller inclination than that in intact plants (cf. Fig. 5). Shading of the inner part only or both of the inner and outer parts of the joint inhibited the blade inclination. When only the outer part of the joint was shaded， inclination was nearly the same as that in non-shaded plants.

In the next experiment. e妊配tof localized irradiation of the explants was examined by giving the blue beam of 1000 erg/cm2/sec for 72 hours. Pr∞edure of experimentation and light sources were sirnilar to those d田cri国dabove. To intercept the scattered light from other direction， whole part of joint in some cases and inner or outer parts of the joint in other ca田 swere painted by blacked vaseline paste. and then different

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on blade inclination of the excised wheat leaves. Explants were taken from the plants cultured in darkness at 2QoC for 8 days. After varlous parts of laminar joint in the explants were painted by black marker， varlous parts of leaves were irradiated with narrow blue beam (10∞erg/cm・/sec)for 72 hours. Q: shows dir田 tionand region of irradiation.

region of the explants were irradia旬dwith blue beam with 2 mm width. The trl回 tmentsare shown shematically in Fig. 8.

The promotive effect of blue 1ight on blade inc1ination was evident only when the laminar joint was exposed to 1ight. In particular， blue 1ight given to the inner part of the joint had strong eff田 t. Irradiation given to the outer part of the joint was also e百'ectiveto some extent， but the blue 1ight given to the blade or the sh回 thhad 1ittle e町ect.

From the results of the舘 experiments，it may be conc1uded that the laminar joint itself is the photo-perceptive organ in inc1ination response， and its inner part is more sensitive than the outer one.

DISCUSSION

Inc1ination respon岱 (photonasticmovement) of the first leaf blade in wheat was observed after 6-day growth in darkness， the maximum respon田 beingobtained on the 9th day. On the 6th day， laminar joint began to appear from the top of coleopti1e. and on the 9th day the leaf sheath alm侶 tstopped the elongation. It is sugg回 tedthat laminar joint itse1f is the site of photoper<句 ptionin photonastic blade movement， and

EU田 tof Light on Leaf Inclination of T，.iticum aostivum 145

that leav白 whoseleaf sheaths have just stopped elongation are most 田 nsitiveto 1ight.

R田 ultsof the pr，白entexperiments in which different regions of the leav白 wereshaded or narrow beam was app1ied to di町'erentregions. also indicated that the laminar joint itse1f is the photo-perceptive organ.

It is well known that the site of photoperception in phototropic r田ponsein伺 tcoleopti1e is the apex of coleoptile (Briggs 1963). In the ca記 oflateral movement of leav田 byasymmetric i11umination in Trotaeolum and Helianthω. the petiole or the blade are most田 nsitiveregion for light perception (Brauner 1954). In tropic turgor movement or nyctinastic movements of釦 meplants. the leaf blade is r白 ponsiblefor the perception of 1ight (Yin 1937). R，叙::ently.Watanabe and Sibaoka (1973) reported that the pulvinule is the only site of photか 限 定ptionto opening r回 pon田 inMimosσl回 flets. Such was not the句記 inwheat plants.

Photonastic movement of wh伺 tleav回 pre詑 ntedhere is irreversible. and differs from nyctinastic movements observed in many plants having pulvinous tissue. Simi1ar photonastic movement of leav田 wasobserved in rice p1ants (Inada 1969).

It is inter;白tingthat e庄町tof blue 1ight given to the inner part of joint was near1y the same as that given to whole開 rtof leaf. This sugg，田tsthat the inner part of joint is the photo舘 nsitivesite. However. 1ight given to the outer part was also somewhat e町'ective. With regard to the e百'ectof 1ight given to the outer part of joint， two explanations areぴ)SSible:1) Outer part of joint is somewhat susceptible to 1ight. 2) Light is transferred from the outer part of the joint to the sensitive inner part. Which alternatives is∞πect. is not determined from the r回 ultsof the pr白 entexperiment.

SUMMARY

1) In wheat seed1ings grown in darkness at 20oC. the inc1ination respon記 ofthe :first leaf blade was observed after 6-day growth in dark-n回 s，and the maximum response was obtained on the 9th day.

2) Appearan偲 ofthe phot国 ensitivitywas accompanied with the appearanαof laminar joint above coleopti1e tip. and the maximum記 n-sitivity was attained when the elongation of the leaf sheath has just stopped.

3) Plants deprived of the apical parts of the blade were sensitive to 1ight in the inc1ination respon詑 tothe回 meextent as that of intact plants.

4) If the laminar joint was shaded by black marker. the inc1ination r田pon田 wasgreat1y inhibited. but the shading given to other regions of the leaf had no e仇ct.

146 K. Kimura

5) Localized irradiation of laminar joint with blue light caused strong blade inclination. The irradiation given to the inner戸rtof laminar joint was more effective than that given to the outer 戸 rt.

6) The blade inclination was observed even in the explants consist-ing of a laminar joint with 5 cm leaf sheath and 5 cm leaf blade， though the response was somewhat lower than that in intact plants.

7) From the results mentioned above， it was concluded that the photosensitive part of 1伺 fin photonastic inclination respon田 ofwheat leaves is laminar joint itself， and its inner part is more sensitive than the outer one.

ACKNOWLEDGMENT

Grateful acknowledgment is made to Prof. A. Takimoto， Kyoto Universlty， for his helpful comments on the manuscript. Sincere gratitude is also due to Miss E. Kimoto for her generous assistance and finally， to Prof. K. Takasu for his constant encour-agement through this work.

REFERENCES

1. Brauner， L. 1954. Tropisms and nastic movements. Ann. Rev. Plant Physio1. 5: 163-182.

2. Brlggs. W. R. 1963. The phototropic responses of higher plants. Ann. Rev. Plant Physio1. 14: 311-352.

3. lnada. K. 1969. Effect of blue light on the photonastic reaction of rice leaves. Plant & Cell Physio1. 10: 845明 954.

4. Kimura， K. 1974. Effect of light on leaf inclination of Triticum aestivum. 1. Mon∞hromatic light. Ber. Ohara Inst. landw. Bio1. Okayama Univ. 16: 47-56.

5. Kimura. K. 1975. Effect of light on leaf inclination of Triticum aestivum. II. Intensity of blue light. Ber.Ohara Inst. landw. Bio1. Okayama Univ. 16: 129-133.

6. Watanabe. S. and Sibaoka. T. 1973. Site of photo-reception to opening r偲 ponsein Mimosa leaf1ets. Plant & Cell Physio1. 14: 1221-1224.

7. Yin. H. C. 1937. Dlaphototropic movement of the leaves of Malva neglecta. Amer. Jour. Bot. 25: 1-6.