Abstract
Suboptimal temperature stress often causes heavy yield losses of vegetables by suppressing plant growth during winter and early spring. Gibberellin acid (GA) has been reported to be involved in plant growth and acquisition of mineral nutrients. However, no studies have evaluated the role of GA in the regulation of growth and nutrient acquisition by vegetables under conditions of suboptimal temperatures in greenhouse. Here, we investigated the roles of GA in the regulation of growth and nitrate acquisition of cucumber (Cucumis sativus L.) plants under conditions of short-term suboptimal root-zone temperatures (Tr). Exposure of cucumber seedlings to a Tr of 16°C led to a significant reduction in root growth, and this inhibitory effect was reversed by exogenous application of GA. Expression patterns of several genes encoding key enzymes in GA metabolism were altered by suboptimal Tr treatment, and endogenous GA concentrations in cucumber roots were significantly reduced by exposure of cucumber plants to 16°C Tr, suggesting that inhibition of root growth by suboptimal Tr may result from disruption of endogenous GA homeostasis. To further explore the mechanism underlying the GA-dependent cucumber growth under suboptimal Tr, we studied the effect of suboptimal Tr and GA on nitrate uptake, and found that exposure of cucumber seedlings to 16°C Tr led to a significant reduction in nitrate uptake rate, and exogenous application GA can alleviate the down-regulation by up regulating the expression of genes associated with nitrate uptake. Finally, we demonstrated that N accumulation in cucumber seedlings under suboptimal Tr conditions was improved by exogenous application of GA due probably to both enhanced root growth and nitrate absorption activity. These results indicate that a reduction in endogenous GA concentrations in roots due to down-regulation of GA biosynthesis at transcriptional level may be a key event to underpin the suboptimal Tr-induced inhibition of root growth and nitrate uptake. These findings may have important practical implications in effective mitigation of suboptimal temperature-induced vegetable loss under greenhouse conditions.
Highlights
Soil temperatures in greenhouses are often changed slowly and maintained at a suboptimal temperature range for growth of horticultural plants in cold seasons, while air temperature can rise suddenly to high temperatures on sunny days [1]
Effects of suboptimal Tr and exogenous Gibberellin acid (GA) application on the growth of cucumber seedlings Previous studies showed that suboptimal root-zone temperate (Tr) suppressed plant growth and productivity by inhibiting root growth and function [3]
To test whether GA is involved in the suboptimal Tr-induced suppression of cucumber growth, we compared growth of cucumber grown at 22°C Tr and 16°C Tr in the presence or absence of GA
Summary
Soil temperatures in greenhouses are often changed slowly and maintained at a suboptimal temperature range for growth of horticultural plants in cold seasons, while air temperature can rise suddenly to high temperatures on sunny days [1]. Suboptimal root-zone temperature (Tr) is one of the major limiting factors for winter horticultural production in greenhouse. Xu and Huang [2] suggested that Tr is more critical than air temperature in controlling plant growth. Low Tr reduces root growth as well as shoots growth even with shoots exposed to optimal temperatures, leading to a heavy loss of crop productivity early in the season when the prices are high [3]. The capacity to assimilate nitrate by cucumber is not affected by low Tr, while low Tr can severely reduce nitrate absorption [9], suggesting that nitrate uptake is a rate-limiting step for N acquisition under low Tr conditions. It has been shown that both root growth and physiology are inhibited by low Tr [3]
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