AMINO-ACID ACCUMULATION IN SINK AND SOURCE TISSUES OF COLEUS-BLUMEI BENTH. DURING SALINITY STRESS

The purpose of this study was to analyse the accumulation of amino aci d in source and sink tissues of variegated Coleus blumei Benth, leaves during an extended exposure to salinity stress, The imposed stress re sulted in a reduction in shoot height and leaf size, as well as a redu ction in total protein and nitrogen content in both the sink and sourc e tissues, At the same time, accumulation of low molecular weight nitr ogen-containing compounds in Coleus leaves was observed, which peaked within the first 10 d of exposure to salinity, and then declined, but remained slightly elevated for the remainder of the study, A number of amino acids were found to accumulate in both the sink and source tiss ues, including arginine, asparagine, and serine, A larger proportion o f asparagine and less arginine was observed in the sink tissue than th e source tissue of the salinity-stressed plants, This difference may r eflect the mobility of these compounds in the phloem, No proline was f ound to accumulate in either the source or sink tissue during the expo sure to salinity, From the pulse-chase labelling of stressed Coleus le aves it can deduced that some of the observed accumulation of amino ac ids and amides observed is due to de novo synthesis and not simply the result of protein degradation.