MOBILE NITROGEN-COMPOUNDS IN SOURCE-SINK SYSTEMS COMPRISING COTTON PLANT OVARIES

The content of main nitrogen compounds (NO3- and NH4+) and free amino acids translocated in cotton plants (Gossypium hirsutum L.) was studie d in the source-sink system comprising a sympodial ovary. A high sink potential of 2- and 4-day old young ovaries determines a much higher l evel of mobile forms of nitrogen (first of all, NH4+) and free amino a cids in the fruit stalk than in the source leaf, in whose axil the ova ry develops. A sharp increase in the ratio of NH4+ to NO3- in the wood of the fruit stalk in comparison with root exudate indicates that som e nitrates en route to the ovary are reduced in the stem and in the xy lem tissue of the fruit stalk. When one of the sympodial ovaries (15-d ay-old) was removed, nitrates were accumulated in the source leaf of t he remaining 2-day-old sympodial ovary within the first day and their reduction was suppressed. It was concluded that the demand of the 15-d ay-old sympodial ovary exerts its effect within a day after the excisi on.