Influence Of Water Deficit On Ear Photosynthesis And Distribution Of Pre-anthesis¹⁴C-assimilates In Wheats With Different Drought Resistances

Drought is an important factor limiting wheat production in China. During filling stage, droughtstress can significantly lower the photosynthetic rate of flag leaf, wheat production. Related studiesshow that non-leaf green organs of wheat also have the ability to produce assimilates. Earphotosynthetic rate is less susceptible to water deficit, which is an important source of grainsassimilates. The growing grains are tightly enclosed by the lemmas and paleas, which are envelopedby the outer glumes. This arrangement of floral tissues may indeed obstruct the exchange of therespiratory CO2with the free atmosphere. Therefore, the study of water deficit on the earphotosynthetic characteristics, distribution of ear assimilates, elaborating photosynthetic carbonfixation and contribution to grain production, are important. Wheats with different drought resistanceswere used in this study. The net photosynthetic rate of the ear, content of soluble sugar andchlorophyll in bracts were measured. Using¹⁴C-photosynthetic label technique, transport ofphotoassimilate was investigated to research photosynthetic contribution of ear to the formation of thegrain. The main results are listed as follows:1. Net ear photosynthetic rates of two wheats with different drought resistances increased firstand then decreased at filling stage. During flowering, net photosynthetic rate of Xinong928decreasedby7.6%under water deficit condition, Zhengyin1decreased by11.6%. These differences were notsignificant. Early grain filling stage （8d after flowering）, decline of ear net photosynthetic rate ofXinong928is not significant under water deficit condition. However, Zhengyin1declinedsignificantly. Xinong928had a relatively high net ear photosynthetic rate under water deficit, net earphotosynthetic rate of Zhengyin1is sensitive to water deficit. The ear photosynthetic contribution tograin is concentrated on early-and mid-filling stage. Then, the contribution of ear photosynthesisdeclined.2. Chlorophyll content of glume continued to rise5days after flowering, then declined. At middlefilling stage（10-25d after flowering）, chlorophyll content of Xinong928glume decreased by53.2%under water deficit, moisture sensitive Zhengyin1fell by84.1%. During filling Stage, lemmachlorophyll conten of both varieties increased first and then decreased. During Middle filling （15dafter flowering）, lemmas chlorophyll content of Xinong928which is under under water deficit, is 6.4%lower than normal water treatment. Lemma chlorophyll content of Zhengyin1decreased by17.8%. It Showed that the glume chlorophyll content decline of Xinong928and lemma are belowZhengyin1, under water deficit conditions. The Xinong928ear managed to maintain a relatively highchlorophyll content and photosynthetic rate under water deficit conditions.3. Total soluble sugar content of glumes in two varieties increased first and then decreased at thegrain filling stage.10d after flowering, total soluble sugar content of Xinong928decreased by2.9%under water deficit condition. The difference was not significant. Moisture sensitive variety Zhengyin1decreased by21.2%, which is a significant difference.10-25d after flowering, total soluble sugarcontent of glume in each treatment continued to decline. Water deficit significantly reduced glumetotal soluble sugar content of Zhengyin1, but Xinong928had no significant effect.4. At early grain filling stage, the¹⁴C-assimilates distribution rate of glume, palea and lemma ineach treatment retreated quickly. Late filling stage,¹⁴C-assimilates distribution rate of glume, paleaand lemma in each treatment stabilized. This suggested labeled¹⁴C-assimilates has been completelytransferred at this time. After harvest, under water deficit condition, the¹⁴C-assimilates distributionrate in glume, palea and lemma of drylands variety Xinong928increased by7%, Zhengyin1decreased8.9%. The difference is significant. Early and medium-term grain filling stage, former¹⁴C-assimilates distribution rate of grain continued to rise. After harvest, under water deficit condition,¹⁴C-assimilates distribution rate of the Xinong928in grain decreased slightly by3.2%, whileZhengyin1increased by7.8%, which is a significant difference. It suggested that moderate waterdeficit promoted rapid transit of¹⁴C-assimilates from glume, palea and lemma to the grain duringfilling stage.5. Water use efficiency of Xinong928rose slightly under water deficit condition, Zhengyin1hada significant drop. Under water deficit condition, Xinong928grain weight, harvest index fellsignificantly, and Zhengyin1drop significantly. Water deficit had limited impact on the Xinong928.