Basis of shoot response to root temperature in tomato

Abstract

Experimental evidence precludes rates of mineral and water absorption as causal factors in the root temperature: shoot growth correlation. When plants were subjected to variations of mineral nutrition or humidity, shoot growth was responsive at a root temperature of 25[degree]C, but almost independent at 15[degree]. Shoot growth of plants growing briefly in distilled water was sensitive to the water temperature and independent of the shoot''s ensuing mineral status. Other evidence was consistent with the foregoing examples. Apparently the phenomenon depends on an unknown endogenous mechanism. A possible mechanism (retarded phloem transport at cool root tempera-ture[forward arrow] congestion of metabolites in shoot [forward arrow] retarded metabolism of shoot cells) is discussed. Root temperature-induced variations of P, K, and NO3 in xylem exudate were not parallel to P, K, and NO3 variations in the intact shoot. Similarly induced variations in plant content of P, K, and Ca under special conditions suggest a pattern of ion loss to the root medium.