Effect of source-sink relations and nitrogen nutrition on senescence and N remobilization in the flag leaf of wheat

Abstract

1991. Effect of source-sink relations and nitrogen nutrition on senescence and N remobilization in the flag leaf of wheat. -Physiol. Plant. 82: 278-284.The relation between the source-sink ratio and nitrogen nutrition on grain yield of wheat (Triticum aestivum L. cv. Klein Chamaco) was studied in a greenhouse experiment. Plants were grown until anthesis in pots with soil fertilized with 0.16 mmol N per plant twice a week. At anthesis, all leaves but the flag leaf were excised in a group of plants. In another group the treatment consisted in a similar defoliation plus the longitudinal excision of half the ear, while a third group was left untouched as a control. At the same time, the N supply to half of the plants in each group was interrupted, while the other half continued receiving 16 mM N. The defoliated plants showed a longer functional life of the flag leaf than the control, retaining the chlorophyll, soluble proteins and total reduced nitrogen for a longer time. The ear-excised plants showed an intermediate behavior. The plants with the interrupted N supply showed a faster leaf senescence than the N supplied ones, and this coincided with an increase in the proteolytic activity and nitrogen transport to the ear. However there were no differences in ear weight between the two nitrogen treatments. It is conciuded that leaves and ear compete for the nitrogen, and that a low level of carbohydrates in the flag leaf, due to a low source-sink ratio, delays leaf senescence.

Crescimento, desenvolvimento e retardamento da senescência foliar em girassol de vaso (Helianthus annuus L.): fontes e doses de nitrogênio

“…Já ao observar-se esse mesmo parâmetro para uma fase mais avançada, em R6, que corresponde ao final da vida de vaso ou capítulo senescente (Figura 1D), verifica-se que a diferença entre as doses caiu para pouco mais de 5%. Esse processo de aceleração da senescência foliar com a maturação da planta é esperado e ocorre devido a altas quantidades de nitrogênio que são mobilizadas das folhas para outros tecidos que estão em crescimento como, por exemplo, as flores (GUITMAN et al, 1991;SMART, 1994;CRAFTS-BRANDER et al, 1998). A senescência das folhas é um fator negativo do ponto de vista da comercialização das plantas de girassol de vaso.…”

“…A remobilização do N na planta inicia com o processo de formação de flores e leva inicialmente à senescência das folhas basais, caracterizada visualmente pelo amarelecimento dessas, seguida de morte (GUITMAN et al, 1991;SMART, 1994;CRAFTS-BRANDER et al, 1998). Na comercialização de girassol em vaso, é comum observar-se folhas basais amarelas, cuja presença afeta o visual e diminui a qualidade do produto, sendo que a diminuição da qualidade é proporcional ao número de folhas senescentes na planta (REID, 2004).…”

Regulation of Photosynthesis during Leaf Development in RbcS Antisense DNA Mutants of Tobacco

“…Consistent with this possibility is the well-established finding that source leaves adjust their photosynthetic rates in response to the demand for photoassimilates in the rest of the plant, inhibiting photosynthesis when the demand is low and increasing photosynthesis when the demand is high (sink regulation of photosynthesis) (reviewed by Turgeon, 1989;von Schaewen et al, 1990;Stitt et al, 1990;Stitt, 1991;Sonnewald and Willmitzer, 1992). It has also been observed that the rate of leaf senescence is affected by the sinksource status of the plant (Christensen et al, 1981;Bin Lazan et al, 1983;Wittenbach, 1983;Shibles et al, 1987;Guitman et al, 1991) and that photosynthetic gene expression can be modulated by carbohydrates at the transcriptional level (Sheen, 1990;Krapp et al, 1993). We are currently investigating the impact of carbohydrate levels on photosynthetic rates and Rubisco gene expression during leaf development in the antisense and WT plants.…”

Photosynthetic Recovery of a Perennial GrassLeymus chinensisafter Different Periods of Soil Drought

“…The tubes were heated in boiling water for 15 min and then rapidly cooled. The absorbance was read at 630 nm (Yemm and Willis, 1954;Güitman et al, 1991). Total soluble sugar content was calculated as the percentage of dry matter of viable leaf.…”