Effects of 6-BA and amino acid selenium on leaf senescence and endoge⁃nous hormones content in grape

Abstract：【Objective】The experiment was conducted to clarify the effects of 6-BA and amino acid sele⁃nium on grape leaf senescence and to provide a theoretical basis for preventing leaves from early aging.【Methods】Two grape cultivars,‘Italia’and‘Centenial’seedless, under protected cultivation for delayedharvest were used for the study. Amino acid selenium and 6-BA were sprayed on the leaves, and sprayingclear water was used as the control group (CK). The physiological indexes, such as chlorophyll content,net photosynthetic rate and endogenous hormone contents were determined during leaf senescence. Theexperiment materials including triennia‘l Italia’and‘Centenial seedless’were planted in key grape tech⁃nique demonstration orchard of Fruit Research Institute of Chinese Academy of Agricultural Sciences(Xingcheng, Liaoning province east longitude 120°06′, northern latitude 40°16′). The plants grafted onBeta rootstock were grown in a solar greenhouse. Tree and row spacing was 2.0 m×0.7 m. A tilt dragontrunk and V form trellis system was adopted with regular managements. Starting from August 1, 2013, thevines were sprayed with 50 mg·L^-1 amino acid selenium [a patented product (ZL201010199145.0) of FruitResearch Institute of Chinese Academy of Agricultural Sciences containing 3% Se, produced by An QiuXin Hai Biofertilizer Limited Company] or 20 mg·L-1 6-BA at 3:00-4:00 pm every 15 days until 15 daysbefore leaf fall. The experimental treatments were set with 3 replicates, each with 15 trees. The concentra⁃tions of amino acid selenium and 6-BA used were based on the results of pre-experiments. Secondly,from September 8th to the end of leaf fall, representative leaf samples from shoots at consistent growthwere taken at 8:00 am every half a mouth. 20 functional leaves located at the 4th to 8th nodes were collect⁃ed, put into a curling stone, and brought to laboratory, where they were frozen with liquid nitrogen. Ace⁃tone soaking methods was used to extract chlorophylls. A CIRAS-2 portable photosynthesis system wasused to measure net photosynthetic rate during a sunny day between 9:00am and 11:00am. The measurements were carried out at a light intensity of 1 200 μmol·m^-2·s^-1, carbon dioxide level of 360 μmol·mol-1and temperature of 25 ℃. ELISA (enzyme linked immunosorbent assay for detection) was used to measuregibberellin (GA3)，zeatin riboside (ZR), auxin (IAA) and abscisic acid (ABA) contents. The ELISA kitswere supplied by Crop Chemical Control Research Center, China Agricultural University. Data collectedwere processed with Excel 2003, and statistic analyses with SPSS 13.0.【Results】Compared with CK, ami⁃no acid selenium and 6-BA treatments significantly delayed the decreases in chlorophyll content and netphotosynthetic rate. With the increase of treatment times, endogenous ZR and GA3 contents and the ratiosof ZR/ABA, GA3/ABA and (ZR+GA3)/ABA increased significantly, while the content of ABA decreasedsignificantly. IAA showed maintained growth in the earlier period but promoted senescence in the later pe⁃riod. Before November 8th, compared with CK, amino acid selenium and 6-BA treatments significantly increased the IAA content in leaves but decreased it later. There were differences in different senescencetypesof grape leaves, the leaves of‘Italia’were slower in senescence with antioxidant enzymes maintain⁃ing higher activities at the late growth stage.【Conclusion】Application of amino acid selenium or 6-BA iseffective to maintain chlorophyll content and net photosynthetic rate in‘Italia’and‘Centenial seedless’grapes and changes the hormone levels and balance. The two reagents can delay leaf senescence and tosome degree prolong the functional period of leaves. Therefore, amino acid selenium and 6-BA application can be an important pratice to delay leaf aging in grapes under protected cultivation for delayed har⁃vest.