Trocas gasosas, fluorescência e níveis de carboidratos em cultivares de soja submetidos a défices hídrico e de fósforo
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2000-11-06
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Universidade Federal de Viçosa
Resumo
Plantas de soja (Glycine max (L.) Merril) foram cultivadas em casa de vegetação, em substrato de solo e areia. Os experimentos foram em fatorial 2 x 2 x 2. O primeiro nível refere-se aos cultivares utilizados (UFV-18 e Doko RC), o segundo à concentração de P (25 mg e 250 mg P dm -3 de substrato) e o terceiro, o estado hídrico da planta (plantas mantidas permanentemente irrigadas e plantas submetidas a déficit hídrico quando as vagens começaram a ser formadas - R3). Um grupo de plantas foi utilizado para a avaliação do efeito do déficit hídrico e um outro grupo para avaliação dos efeitos do ressuprimento de água. Verificou- se redução da taxa fotossintética líquida sob condições de deficit de água. A deficiência hídrica não alterou a eficiência quântica do fotossistema II, medido pelas razões Fv/Fm, Fv’/Fm’ e φFSII, e nem a dissipação não-fotoquímica (qNP), exceto quando em interação com a deficiência de fósforo. Em função do déficit hídrico, ocorreram diminuição na condutância estomática e na taxa transpiratória. O teor de amido foliar foi reduzido e a atividade da pirofosforilase do ADPG não foi alterada, enquanto os teores de açúcares não-redutores, redutores e solúveis totais foram aumentados em função da deficiência hídrica. A massa seca das folhas e da parte aérea das plantas só sofreu redução nas plantas do cultivar Doko RC cultivadas no nível mais alto de fósforo. Sob deficiência de fósforo, a queda da taxa fotossintética líquida foi acompanhada por redução na eficiência quântica fotoquímica e por aumento na dissipação não-fotoquímica da energia radiante. Grande parte dessa dissipação não-fotoquímica foi na forma de calor. O efeito da deficiência de fósforo na condutância estomática foi ambivalente, a razão C i /C a aumentou, enquanto o teor de Pi foliar foi drasticamente reduzido e os teores de clorofilas sofreram redução apenas no cultivar Doko RC. Sob déficit de fósforo, os teores de amido foliar e a atividade da pirofosforilase do ADPG foram aumentados e, de maneira geral, os teores de açúcares não-redutores, redutores e solúveis totais não foram alterados. Ocorreram ainda, reduções acentuadas da massa seca das folhas e da parte aérea das plantas. A reirrigação praticamente não afetou os mecanismos dissipativos da energia não-fotoquímicos. Após a reirrigação, houve recuperação da taxa fotossintética líquida, da condutância estomática, da taxa transpiratória e da relação C i /C a , com valores iguais aos das plantas-controle. Também, os teores de todos os açúcares analisados foram semelhantes após a reirrigação, com exceção das plantas que sofreram deficiências combinadas.
Soybeans plants, Glycine mm: (L.) Merril. were grown in greenhouse conditions, in a soil and sand substratum. Experiments were conducted in a factorial 2 x 2 x 2 design, referring to two cultivars (UFVaIS and Doko RC) two P levels (25mg and 250 mg P dm’3 substratum) and to plant water status (plant permanently irrigated and submitted to a water deficit when pods were initiated - R3). A group of plants was employed as for evaluation of the effects of the water deficit and another one for evaluation as for the effect of the water ressuply. A decrease in the rate of net photosynthesis under conditions of water defiti was observed. The water deficit did not affect either the quantum efficiency of photosystem II or the non-photoehemical dissipation of the absorbed energy (qNP). except when in co-action with a P deficiency. A decrease in stomatal condutance and transpitation rate as related to water deficit was also observed. Starch levels in leaves were decreased, ADPG pyrophosphorilase activity was not altered and reducing. non-reducing and total soluble sugars were increased in relation to water deficits. Leaf and shoot dry matter was decreased only in plants of cv Doko RC grown under higher P levels. Under a P deficiency, the fall in rate of net photosynthesis was accompanied by a reduction in photochemical quantum efficiency and by an increase in the non-photochemical dissipation of energy. A large part of this non-photochemical dissipation occurred in heat form. The effect of P deficiency on stomatal conductance did not show any consistent pattern, the (Ti/Ca ratio increased, whilest the levels of leaf Pi were drastically reduced and chlorophyll contents were decreased only in cv Doko RC. Under a P deficit, leaf starch and ADPG pyrophosphorilase activity were increased and, in a general way, the levels of not-reducing, reducing and total soluble sugars were not affected. Accentuated reductions in leaf and shoot dry matter were observed. Re-irrigation practically did not affeCt the dissipating mechanisms of non- photochemical energy. Following re-irrigation recoveries in the rate of net photosynthesis, stomatal conductance, transpiration rates and in the Ci/Ca ratio to the extent of control values occurred. Also, the contents of all sugars showed similar to controls following re-irrigation, except for the plants suffering a combined water and P deficiency.
Soybeans plants, Glycine mm: (L.) Merril. were grown in greenhouse conditions, in a soil and sand substratum. Experiments were conducted in a factorial 2 x 2 x 2 design, referring to two cultivars (UFVaIS and Doko RC) two P levels (25mg and 250 mg P dm’3 substratum) and to plant water status (plant permanently irrigated and submitted to a water deficit when pods were initiated - R3). A group of plants was employed as for evaluation of the effects of the water deficit and another one for evaluation as for the effect of the water ressuply. A decrease in the rate of net photosynthesis under conditions of water defiti was observed. The water deficit did not affect either the quantum efficiency of photosystem II or the non-photoehemical dissipation of the absorbed energy (qNP). except when in co-action with a P deficiency. A decrease in stomatal condutance and transpitation rate as related to water deficit was also observed. Starch levels in leaves were decreased, ADPG pyrophosphorilase activity was not altered and reducing. non-reducing and total soluble sugars were increased in relation to water deficits. Leaf and shoot dry matter was decreased only in plants of cv Doko RC grown under higher P levels. Under a P deficiency, the fall in rate of net photosynthesis was accompanied by a reduction in photochemical quantum efficiency and by an increase in the non-photochemical dissipation of energy. A large part of this non-photochemical dissipation occurred in heat form. The effect of P deficiency on stomatal conductance did not show any consistent pattern, the (Ti/Ca ratio increased, whilest the levels of leaf Pi were drastically reduced and chlorophyll contents were decreased only in cv Doko RC. Under a P deficit, leaf starch and ADPG pyrophosphorilase activity were increased and, in a general way, the levels of not-reducing, reducing and total soluble sugars were not affected. Accentuated reductions in leaf and shoot dry matter were observed. Re-irrigation practically did not affeCt the dissipating mechanisms of non- photochemical energy. Following re-irrigation recoveries in the rate of net photosynthesis, stomatal conductance, transpiration rates and in the Ci/Ca ratio to the extent of control values occurred. Also, the contents of all sugars showed similar to controls following re-irrigation, except for the plants suffering a combined water and P deficiency.
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Palavras-chave
Soja, Fósforo
Citação
BEZERRA, Marlos Alves. Trocas gasosas, fluorescência e níveis de carboidratos em cultivares de soja submetidos a défices hídrico e de fósforo. 2000. 86 f. Tese (Doutorado em Fisiologia Vegetal) - Universidade Federal de Viçosa, Viçosa. 2000.