Inhibition effect of high strength nutrient solution on hypocotyl stretch of cucumber and tomato seedlings
Objectives]Cucumber (Cucumis sativus) and tomato (Lycopersicon esculentum) are main cultivated vegetable species in China. The seedling growth in breeding processes is vulnerable to disadvantageous environments, such as high temperature, high humidity and weak light, which lead to excessive hypocotyl stretch and reduce yield at later stage.Several methods such as plant growth regulators, mechanical stimulations, supplement of light, temperature modulation and water limitation are used to prevent excessive hypocotyl stretch, but the effects are always not satisfied due to complicated influence factors.To develop an effective method for controlling hypocotyl stretch in cucumber and tomato seedlings, this paper focused on the inhibition effect of high strength nutrient solution on hypocotyl stretch in cucumber and tomato seedlings.[Methods] A concentration of complete macroelement of 1.0 strength Hoagland nutrient solution was defined as fundamental formula ( 1.0 C ) . Other nutrient solution concentration gradients involved in this experiment were 0.5, 2.5, 5.0, 7.5, 10.0 and 12.5C by adding macroelement compositions proportionally without changing the microelements compositions.The 0.5C nutrient solution was set as the control group, and others were the treatment groups.After watering cucumber and tomato seedlings by different nutrient solutions in greenhouse conditions, the growth parameters were measured, and the nutrient solution effects on hypocotyl cortical cell length, growth rate and phytohrmone levels were determined at the cytoledon extending stage.Then seedlings were rewatered by the 0.5C nutrient solution to restore the inhibition growth of hypocotyl stretch.The growth parameters were measured at the first true leaves extending stage.The effects and mechanism of high nutrient solution on inhibiting hypocotyl stretch were determined, and the optimal strength was acquired by appropriate effect on cucumber and tomato seedlings.[Results]The effects of six strength ( 0.5, 2.5, 5.0, 7.5, 10.0 and 12.5C ) Hoagland ’ s nutrient solution on controlling the excessive hypocotyl stretch are:1) The electrical conductivity (EC) of substrate increases linearly (r=0.99) and growth of both cucumber and tomato are inhibited gradually from 0.5C to 12.5C nutrient solution.Compared with the 0.5C nutrient solution, the lengths of hypocotyl cortical cell are decreased by 49% in cucumber and 48% in tomato under the 10.0C nutrient solution.2) The endogenous phytohormone homeostasis is disturbed by decreasing GA3 and ZR levels but increasing ABA level which significantly displays a negative correlation with hypocotyl length ( P<0.01 ) .The IAA level shows different tendency dependent on the concentration of nutrient solution.3 ) The growth of hypocotyl stretch that has been inhibited by high strength of nutrient solution could be restored to different degrees by rewatering 0.5C nutrient solution.Especially in the 5.0C and 7.5C treatments, the ratios of plant height/stem diameter are better than those in other treatments, which could be expected to effectively control excessive hypocotyl stretch.[Conclusions] High strength nutrient solution contributes to the inhibition effect on excessive hypocotyl stretch by changing endogenesis phytohormone homeostasis, apparently because of promoting more ABA synthesis and accumulation in hypocotyl cells, and shortening hypocotyl cortical cell length.The inhibition effect could be restored by decreasing the nutrient solution concentration.The method exhibits potential application prospect due to simple maneuverability and obvious effects, but the optimal strength and mechanism on different vegetable species still should be further studied and analysed.
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