Cytokinins in Enhanced Growth and Tillering of Wheat Induced by Mixed Nitrogen Source

Abstract

Supplying wheat plants with mixtures of NO~-and NH4 + increases growth and tiller production, but the physiological basis is unclear. Our objectives were to evaluate the roles for cytokinins and N use (e.g., accumulation, distribution, and utilization of absorbed N to produce tillers) in eliciting this response. Two species of spring wheat (Triticum aestivum L. cv. Len and Triticum durum Desf. cv. Inbar) were grown hydroponically in the greenhouse with N supplied as all NO~-, all NH4 + , or an equal mixture of each form. In one experiment, the synthetic cytokinin N6-benzylaminopurine (100 pM) was applied repeatedly (a total of five times) to the shoots during tiller initiation and development, while in another, xylem exudate was collected from cut stumps during the early stages of tiller development. Plants not sprayed with cytokinins produced more tillers and accumulated more N when grown with mixed N than with either N form alone. Cytokinin sprays did not affect tillering of mixed N plants but increased tillers in all-NOr-grown or alI-NH~+-grown plants to levels close to that obtained with mixed N. For unsprayed plants, the presence of NH~ increased the shoot/root ratio, the proportion of N in the shoot, and the efficiency with which absorbed N was used to produce tillers, compared with plants grown with all NOa-. Exogenous cytokinin appeared to mimic the effects of mixed N (and in some cases NH4 +) in altering the distribution and use of N by the plant. In addition, plants grown with mixed N or all NH4 + exhibited higher concentrations and mass transfer of cytokinins in the xylem than those supplied with all NO~-. These data are consistent with the interpretation that mixed N enhancement of tillering in wheat is due to increased synthesis of cytokinins, induced in part by use of NH4 +-N. F OR CEREAL CROPS such as wheat, the number of ears per plant is determined by the extent of lateral bud growth. This number depends on the species, the cultivar, the size and vigor of the seed, and various environmental factors such as light intensity, photoperiod, temperature, and availability of water and mineral nutrients during the period of tiller formation (Simons, 1982). Cytokinins are also known to be associated with the growth and development of tiller buds (

Combined effects of contrast between poor and rich patches and overall nitrate concentration on Arabidopsis thaliana root system structure

“…This is in accordance with the fact that in high nutrient concentration situations the general trend is a decrease in root length and number of ramification at excessive nutrient supply. The most common response to an increase in nitrate and ammonium concentration in the environment is a decrease in root : shoot ratio (Boxman et al 1991;Wang and Below 1996;Bauer and Berntson 1999) and a decrease in fine : coarse root ratio (Haynes and Goh 1978;Boxman et al 1991;Britto and Kronzucker 2006), as observed here.…”

O afilhamento da aveia afetado pela qualidade da luz em plantas sob competição

“…A giberelina, porque pode alterar o alongamento celular em função de efeitos da qualidade da luz (WELLER et al, 1994;FOSTER et al, 1994;LÓPEZ-JUEZ et al, 1995;REED et al, 1996) e a citocinina por estimular a iniciação da divisão celular em afilhos (WANG & BELOW, 1996). Outra possibilidade é o fato de o fitocromo estar envolvido no controle de genes ligados à fotossíntese, codificando a síntese de clorofila a/b, pequenas subunidades da Rubisco e outros componentes do maquinário fotossintético (DALE, 1988).…”

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

“…Moreover, it is found that there is a marked difference among N forms in their effects on growth and chemical composition of crop plants (Cramer and Lewis 1993). The physiological processes in plants, such as root respiration (Matsumoto and Tamura 1981), photosynthesis (Shelp and Taylor 1990), and secondary metabolism (Wang and Below 1996) are also dramatically associated with N form. Thus it is possible that Cd uptake and translocation in the plants will be affected by N form in the nutrient medium.…”