Bedeutung einiger nichtflüchtiger carbonsäuren für die frostresistenz des halophyten Halimione portulacoides unter dem einfluß verschieden hoher kochsalzbelastung

Abstract

Plants of Halimione portulacoides (L.) Aellen were grown in natural temperature and light conditions but with different concentrations of NaCl in the nutrient solution. From August 1971 to April 1972 freezing tolerance, water content, succulence, accumulation of different sugars, citrate, malate, and chloride were simultaneously determined. If no NaCl was supplied the chloride content of the leaves decreased continuously within the period of investigation. During repeated and increasing addition of NaCl the chloride content of the leaves generally increased. However, there was a reversible decrease during the frost period, although no new leaves were formed and loss through leaves and dilution of the nutrient medium by precipitation was prevented (Fig. 1).In spite of being in minimum the chloride content was relatively high in winter. No regulation of the concentration by increase of succulence was observed. The concentration did, however, increase due to a diminished water uptake in the coldest period.Sugars, which are regarded as protective agents against the influence of freezing and salts, accumulated only slightly in the frost period. Predominantly sucrose, raffinose and stachyose were remarkable. Their concentration was not sufficient to compensate the salt burden and thus could not increase the freezing tolerance. The sugar content was even lowered when the salt content was higher. In contrast, citrate and to a lesser extent malate were intensively increased in the cold season (Fig. 3). Thus organic acid to chloride ratios of between 1:2 and 1:6 were established for Halimione, which expresses the effective protection of the membrane systems against freezing injury (Fig. 4), as has been shown in vitro for e.g. spinach chloroplasts by Santarius (1971). Accumulation of these acids was even enhanced by an increasing salt burden. Consequently accumulation of organic acids or their salts such as citrate and probably malate indicates an adaptation of halophytes, which enables them to survive freezing under salt stress on the sea shore and in cold desert regions during the winter.