Sugar repression of photosynthesis: the role of carbohydrates in signalling nitrogen deficiency through source:sink imbalance

Abstract

The aim of this work was to examine whether carhohydrates are involved in signalling N deficiency through sourcersink imbalance. Photosynthetic metaholism in tohacco was studied over 8 d during the withdrawal of N from previously N-sufficient plants in which the source:sink ratio was manipulated hy shading leaves on some of the plants. In N-sufficient plants over this timescale, there was a small decline in photosynthetic rate, Ruhisco protein and amino acid content, with a larger decrease in carhohydrate content. Withdrawal of N from the growing medium induced a large decrease in the rate of photosynthesis (35% reduction after 8 d under the growing conditions, with a reduction also apparent at high and low measuring CO2), which was caused hy a large decrease in the amount of Rubiseo protein (62% after 8 d) and Ruhisco activity. Higher amounts of hexoses preceded the loss of photosynthetic activity and sucrose and starch accumulation. Reduction of the sourcersink ratio hy shading prevented the loss of photosynthetic activity and the increase in hexoses and other carbohydrates. These data indicate that the reduction of photosynthesis that accompanies N deficiency in intact plants has the characteristics of sugar repression of photosynthesis observed in model systems, but that the accumulation of hexose prior to the decline in photosynthesis is small. The possibility that sugar repression of photosynthesis under physiological conditions depends more crucially on the C:N status of leaves than the carbohydrate status alone is discussed.

Nitrogen Supply Influences Herbivore-Induced Direct and Indirect Defenses and Transcriptional Responses in Nicotiana attenuata

“…7). Higher concentrations of soluble sugars such as Glc, Fru, and Suc, in the leaves of LN plants (Rufty et al, 1988;Paul and Driscoll, 1997) are known to enhance the expression of wound-induced PI genes as well as the expression of vegetable storage proteins in other species (Johnson and Ryan, 1990;Mason et al, 1992). A similar disconnect between metabolite and transcript accumulation was found in the accumulation of phenolic metabolites (chlorogenic acid and rutin) and their associated biosynthetic transcripts (Fig.…”

Populus deltoides females are more selective in nitrogen assimilation than males under different nitrogen forms supply

“…The accumulation of starch at low N is a well-established phenomenon (Rufty et al 1988;Paul and Stitt 1993;Paul and Driscoll 1997). Thus, the increasing nitrogen supply using nitrate, ammonium or ammonium nitrate, all resulted in lower starch concentrations in the present paper.…”

Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings II. Photosynthetic capacity and water relations

“…Starch accumulation in leaves, by maintaining stromal P i cycling, allows A to continue unchanged (Stitt, 1991), and by lowering the amount of soluble sugar in the cytosol reduces the source of the regulatory signal that, according to Van Oosten & Besford (1996), might effect coarse control of the photosynthetic genes. Paul & Driscoll (1997), by manipulating the source-sink ratio of Nicotiana tabacum, found that the loss of photosynthetic activity was more correlated to the hexose : amino acid ratio than to sugar concentration per se, and concluded that the regulatory signal causing repression of A depends more crucially on the carbon : nitrogen ratio than on the carbohydrate status of leaves. Accordingly, the increased leaf carbon : nitrogen ratio, i.e.…”