Effects of Water Stress on Growth, Photosynthesis, Root Activity and Endogenous Hormones of Cucumis sativus

A greenhouse experiment was conducted to investigate the effects of water stress on growth, photosynthesis, root activity and endogenous hormones of cucumber (Cucumis sativus L. var. Boxin 525). Three water stress levels were involved in the experiment: mild water stress (T1, relative soil water content (RSWC) was 60-70%), moderate water stress (T2, RSWC was 50-60%), and severe water stress (T3, RSWC was 35-45%); cucumber plants being irrigated adequately served as the control (CK, RSWC was 70-80%). The results suggested that the plant height, leaf area per plant, root length and root dry weight decreased with increasing water stress levels. The plant height at 60 days after transplanting (DAT) decreased by 5.00%, 25.13%, and 49.75% under T1, T2 and T3, respectively, compared to CK. The leaf area per plant under CK was more than double of that under severe water stress. The average decreasing amplitude of root length was 26.26, 42.91 and 66.92% with increasing water stress levels, compared to CK. In the same way, root dry weights were decreased on average by 13.89, 30.88 and 47.52%, respectively. Water stress reduced the net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (E) at 20, 30, 40, 50 and 60 DAT under T1, T2, and T3. Compared to CK, the average Pn of cucumber leaves over the entire growth stage decreased by 9.27%, 27.86% and 42.37%, respectively. The gs values under CK were almost 1.18, 1.20 and 1.36 times of that under T1, T2 and T3, respectively. The average E in CK plants was 10.23 mmol (H2O) m(-2) S-1, while it ranged from 5.83 to 9.22 mmol (H2O) (H2O)m(-2) S-1 Under different water stress conditions. The root activity of cucumber plants declined by 13.04%, 26.57% and 34.41% with increasing water stress levels, respectively. The zeatin nucleoside (ZT) in cucumber leaves decreased with the aggravation of soil water stress, with the average reduction amplitude being 14.65%, 28.93% and 38.62% compared to CK, respectively, for T1, T2 and T3, while the abscisic acid (ABA) contents in cucumber leaves rose as the water stress increased at 20, 30, 40, 50 and 60 DAT. Compared with CK, the ABA contents were elevated by 58.45 and 107.66%, respectively, under moderate water stress and severe water stress. Mild water stress reduced the gibberellin (GA(3)) concentration, except at 20 DAT. The GA(3) levels reached their peaks at 60 DAT for all treatments, with the peak value for T1 rising by 5.73%, and those for T2 and T3 reducing by 21.53 and 36.21%, respectively, compared to CK. The auxin (IAA) contents increased under both mild water stress and moderate water stress over the whole stage, while those under severe water stress were the lowest among all treatments. Water stress reduced the ZT/ABA, IAA/ABA, ZT/IAA, and (GA(3) + ZT + IAA)/ABA ratios in cucumber leaves. Compared with CK, the GA(3)/ABA ratio decreased under moderate water stress and severe water stress, while no significant difference in the GA(3)/ABA ratio was found between mild water stress and CK, with an exception at 20 DAT. Water stress decreased growth traits and root activity of cucumber plants, affected leaf gas exchange parameters. The changes of endogenous hormone and the ratio between different endogenous hormones could resist the adversity of water stress and affect the growth and development of crops. (C) 2018 Friends Science Publishers