Accumulation of Proline, Flavonoids, and Organic Acids in Cress Leaves under Conditions of Salt-Alkaline Stress

The authors studied changes in the content of proline, flavonoids, and organic (malic, citric, succinic) acids in watercress plants ( Lepidium sativum L.) at the initial stage of development of salt-alkaline stress. The two-factor experiment included variants with NaCl salinity (50, 100, 150, 200 mM), alkalinity (at pH = 7–10) and variants of combined effects of salt and pH. The separate and mutual effects of stress factors on changes in the height and weight of the above-ground parts of plants; water, Na + , proline, flavonoids, content; and total organic acids in the leaves were determined using two-factor analysis of variance with determining the strength of influence according to Snedecor. Changes in the height and weight of watercress were minimal 24 and 48 h after stress exposure, and the strength of the influence of stress factors was no more than 4–7%. The water content of watercress leaves has decreased; these changes are due to the separate and mutual effects of NaCl salinity and high pH values by 35–53%. A noticeable accumulation of Na + was observed in the leaves of watercress; its content in the first hours of observation depended on the individual influence of stress factors. After 24 h, the amount of Na + in leaves increased several times relative to the control, the indicators of individual and mutual influence of salt-alkaline stress factors reached 31–33%. The accumulation of proline in leaves depended to a greater extent on salinity and the mutual action of stress factors (influence within 26–33%). The influence of high pH values did not exceed 21%. A slight accumulation of flavonoids was noted only 1 h after stress exposure. It was found that the increase in the total content of citric, malic, and succinic acids depended equally on the individual and mutual influence of factors; the total effect of NaCl salinity and high pH values reached 97–99%. Thus, under conditions of salt-alkaline stress, the accumulation of organic acids and proline is the basis of adaptation processes in watercress.