Exogenous application of phytohormones mitigates the effect of salt stress on Carica papaya plants

ABSTRACT The salinity has complex effects on the physiological, nutritional and hormonal interactions of plants. This study aimed to evaluate the mitigating action of exogenous application of different types and concentrations of phytohormones on Carica papaya under salt stress. The experiment was conducted in greenhouse, using a randomized block design with treatments formed from a 2 x 3 x 5 factorial scheme, relative to two concentrations of salts in the irrigation water (0.6 and 2.4 dS m-1), three types of phytohormones [Auxin = indole-3-acetic acid; Cytokinin = CPPU (N-(2-chloro-pyridyl)-N-phenylurea) and Gibberellin = gibberellic acid(AG3)], and five concentrations of the phytohormone (0, 12.5, 25.0, 37.5 and 50.0 µM L-1), with three repetitions, totaling 90 plots, and the experimental unit consisted of six plants. C. papaya cv. ‘Sunrise Solo’ was grown on polyethylene trays of 162 cells, with capacity for 50 mL. The plants were evaluated for survival percentage and phytomass accumulation until 25 days after sowing. Increase in irrigation water salinity has deleterious effects on C. papaya plants regardless of the application of phytohormones. Exogenous application of gibberellin has a positive effect in mitigating salt stress on C. papaya plants, greater than the effects of auxins and cytokinins. Exogenous application of gibberellin and auxin at concentration of 37.5 µM L-1 mitigates the effects of salinity on C. papaya plants. Exogenous application of cytokinin at concentrations of 12.5 to 50.0 µM L-1 is not viable for C. papaya plants.

摘要
盐度对植物的生理、营养及激素互作存在复杂调控作用。本研究旨在探究外源施用不同类型与浓度的植物激素，对盐胁迫下番木瓜（Carica papaya）的缓解效应。试验于温室环境中开展，采用随机区组设计，处理组设置为2×3×5析因试验方案：包含灌溉水盐度2个梯度（0.6与2.4 dS·m⁻¹）、3种植物激素[生长素（Auxin）：吲哚-3-乙酸；细胞分裂素（Cytokinin）：CPPU（N-(2-氯吡啶基)-N-苯基脲）；赤霉素（Gibberellin）：赤霉素（AG3）]，以及5种植物激素施用浓度（0、12.5、25.0、37.5与50.0 µM·L⁻¹），每组设置3次生物学重复，总计90个试验小区，每个试验单元包含6株植株。试验采用162孔、单孔容积50 mL的聚乙烯育苗盘栽培番木瓜品种‘日出独奏’（Sunrise Solo）。于播种后25天，测定植株的存活率与生物量积累量。结果显示：无论是否施用植物激素，灌溉水盐度升高均会对番木瓜植株产生不利影响；外源施用赤霉素可显著缓解番木瓜遭受的盐胁迫，其效果优于生长素与细胞分裂素；以37.5 µM·L⁻¹浓度外源施用赤霉素与生长素，可有效减轻盐胁迫对番木瓜植株的伤害；而以12.5~50.0 µM·L⁻¹浓度外源施用细胞分裂素，对番木瓜植株无缓解盐胁迫的效果，甚至不具备应用可行性。