Effects Of Water Stress On Photosynthetic Characteristics Of Different Leaf Age Leaves Of Cabernet Sauvignon Grape

In order to study the effect of water stress on photosynthetic characteristics of different leaf age of Cabernet Sauvignon grape.Taking 3 years-old"Cabernet sauvignon"as the experimental material,control?moderate and severe 3 water treatments were set based on the pre-dawn leaf water potential((?)b).The experiments studied the effect of water stress on photosynthetic characteristics for grape shoots basal(leaf 1:leaf expansion on April 20),lower(leaf 2:leaf expansion on April 30),middle(leaf 3:leaf expansion on May 10),upper-middle(leaf 4:leaf expansion on May 20),upper(leaf 4:leaf expansion on May 20)with the increase of leaf age.The results showed as follows:1.The Pn,Tr and Gs of leaves in each part of Cabernet sauvignon,with the increase of leaf age,changed as a single peak curve after silking.The Pn of leaves 1-5 peaked at leaf ages of 90d,80d,70d,60d and 50d and the Pn was close to 0 for leaf 1 at leaf age 135d.Cluster analysis showed that the Pn of leaf 3(70d),leaf 4(45-60d),leaf 5(50d)were at a high level;leaf 1(105-135d),leaf 2(110?125d)was at a low level;other leaf age leaves were at a middle level.Under water stress,the WSD of Cabernet sauvignon increased gradually and photosynthetic parameters decreased to different degrees and leaves 1 and 5 were the most affected.Severe stress seriously affected the normal growth and development of leaf 3,4 and 5,and significantly reduced leaf area.2.The SPAD values of leaves 1?4,with the increase of leaf age,increased firstly and then decreased,while leaf 5 increasing successively.The FvFm,Yield,ETR,and qP of leaves 1-5 increased rapidly and then decreased,and reached the maximum during the leaf ages of 90d,65-95d,70?85d,60?75d,and 50?65d.Water stress increased the value of NPQ and decreased the FvFm,Yield,ETR and qP and leaf 1 and 5 decreased the most under severe stress.However,the FvFm,Yield,ETR of leaf 3increased by 2.30%,22.20%and 23.26%at leaf age of 115d,respectively.3.With the increase of leaf age,Rubisco and FBPase activity of leaves 1?5 increased gradually and reached the maximum at leaf age of 90d,80d,70d,60d,65-50d and then gradually decreased;The content of chlorophyll a and b in leaves 1 and 2 and the total content of chlorophyll began to decrease after leaf ages of 75d and 65d.The photosynthetic key enzymes activity of cabernet sauvignon leaves decreased to different degrees under water stress and the difference between moderate and control was not significant,while the activity of enzymes decreased significantly under severe stress.The activity of SOD,POD and CAT in leaves increased to different degrees under water stress,while the activity of POD in leaves 1?5 was significantly lower than that of control during the leaf ages of 105?120d,95?110d,100d,90d and 65?80d.The content of carotenoids increased in all leaves except leaf 1 under water stress,and the content of chlorophyll in leaves 1?4 increased under moderate stress,and the content of chlorophyll decreased significantly under severe stress.4.With the increase of leaf age,sucrose content of leaves 1?2 decreased after leaf age of 105d and 95d,while sucrose content of leaves 3?5 increased successively and the starch content reached the maximum when the leaf ages were 105d,110d,85d,90d and 80d of leaves 1?5.Under water stress,the starch content of leaves decreased gradually,and the content of reducing sugar and soluble total sugar increased gradually.The sucrose content of leaves 1?5 under moderate stress increased by 26.43%,1.74%,34.72%,0.16%,35.19%and 2.23%at leaf ages of 75d,95d,100d,90d,35d and 80d,respectively,and significantly decreased under severe stress.Under water stress,the SPS activity of leaves in each part decreased,and the SS,AI and NI activity increased,but the SS and NI activity of leaf 1 was lower than that of control at leaf age 105-120 d.In summary,the photosynthetic function of Cabernet sauvignon leaves increased rapidly after leaf expansion,the curve changes as a single peak,and the leaves in different parts are different and the photosynthetic capacity of the upper and middle part of the leaves was relatively strong.Moderate water stress can improve the photosynthetic efficiency of the leaves to some extent,while severe stress not only reduces the photosynthetic efficiency of the leaves,but also accelerates the senescence of the leaves at the base of the new tips and hinds the normal growth and development of the upper segment slices.