Abstract
In this research, was used four papaya (Carica papaya L.) genotypes: three from the 'Solo ( Sunrise Solo TJ, Sunrise Solo 72/12 and Baixinho de Santa Amália) group and one from the 'Formosa' group (Know-You 01). They were grown in plastic pots containing a sandy-clay-loam soil subjected to pH correction and fertilization, under greenhouse conditions. Throughout the experimental period plants were subjected to periodic irrigation to maintain the soil humitidy around field capacity. The experiment was conducted 73 days after sowing. In all genotypes, leaf gas exchange characteristics were determined. The net photosynthetic rate (A, mumol m-2 s-1 ), stomatal conductance (g s mol m-2 s-1), leaf temperature (T I, 0C) and intercellular carbon dioxide concentration (ci, muL L-1) on the 4th, 5th, 6th, 7th, 8th and 9th leaves from the plant apex were determined. No significant differences were observed for A, g s, c i, or Tl either among the leaves sampled from any of the genotypes. A was positively correlated with g s and in the other hand T I and g s were negatively correlated. The results suggest that, for 73 DAP, all the sampled papaya leaves functioned as sources of organs.
Highlights
During leaf expansion the net photosynthetic rate (A)reaches a maximum value before maximum leaf area is reached and decreases after leaf maturity
The results suggest that, for 73 dias após o plantio (DAP), all the sampled papaya leaves functioned as sources of organs
The increase in the net photosynthesis rate is related to several events linked to leaf development: increase in leaf area, leaf thickness, surface and volume of mesophyll cells, leaf inner surface and the dimensions of leaf chloroplasts (Catský & Sesták, 1997)
Summary
During leaf expansion the net photosynthetic rate (A). Reaches a maximum value before maximum leaf area is reached and decreases after leaf maturity. The increase in the net photosynthesis rate is related to several events linked to leaf development: increase in leaf area, leaf thickness, surface and volume of mesophyll cells, leaf inner surface and the dimensions of leaf chloroplasts (Catský & Sesták, 1997). The pigment contents, stomatal mesophyll conductance increases during leaf development. The activity of photosynthetic enzymes increases along with the photochemical processes such as light harvest, electron transport chain activity and phosphorylation. The leaf photosynthetic apparatus is completely developed and the maximum A value is reached when the leaf has 35 to 100% of its maximum area. The decrease in A, at senescence, is associated to the decrease in both stomatal and mesophyll conductance (Catský & Sesták, 1997)
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