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.