Temperature dependence of photosynthate partitioning in intact leaf tissue of tomato {Lycopersicon esculentum Milí. cv. Abunda) was studied by using a temperature gradient cuvette systém. At the low photon flux density (PFD, 85 pmol m*2 s**) and saturated CO2 concentration, the total saccharides production was similar over the temperature range from 14 to 30 «€. The starch foímation decreased with decreasing temperature. Formation of the soluble saccharides was affected by the temperature only slightly. This differential effect of the temperature resulted in an increase of the soluble saccharides/starch ratio in tomato leaves under chilling conditions.
The aim of ťhis study was to clarify whether there are generál differences between the woody and herbaceous plants in their responses to a single non-lethal freezing stress, when measured under comparable conditions. Activity of net photosynthesis (^N33)» th® curves of versus photosynthetic photon fluence density and versus intercellular partial pressure of CO2, and ratio of variable to maximal fluorescence (F^Fm) were measured at optimal temperatures in the leaves of six woody and six herbaceous plant species prior to frost-hardening, after frost-hardening at low positive temperatures and after a single over-night freezing stress (-10 ®C, 12 h) of the shoots. Recovery of at 20/15 “C was also followed. There were no generál differences between woody and herbaceous plants in their photosynthetic responses to freezing stress. In most plants, Pn33 was strongly reduced after freezing mainly due to the disturbances in fimctioning of the chloroplasts, but it recovered within a few days. However, of some herbaceous plants (Cochlearia, one cultivar of spinách) was insensitive to non-lethal freezing. Furthermore, stomatal opening of a few herbaceous plants (Cochlearia, Valerianella) was disturbed after freezing without any sign of an impairment in fimctioning of the chloroplasts.
Rates of the net photosynthetic CO2 uptake the import of '“♦C-labelled assimilates in developing groundnut leaves on the 5"’, 9‘*' and I6"i positions from the stem base were followed over a 20 d maturation period. Maximum import of labelled assimilates into the leaf was observed on the 2"^ day after leaf emergence, when the developing leaf had attained 10-12 % of its fmal leaf area (% Aj). Thereafter, by the day the •‘^C-import rate declined rapidly and asymptotically to a near zero value. The rapid decline in import was offset by a rapid rise in /’n. Pjsj was first observed at 20-30 % Af. Maximum values were attained by the 6‘*’ day, irrespective of leaf area attained by the developing leaves, and were maintained up to the end of the experiment.
Net photosynthetic rate {P^) of Brassica carínata strains, synthesized froin the reciprocal cytoplasms, i.e. B. carinata-226 (B. nigra x B. oleracea) and naturally occurring B. carínata which cairies B. nigra cytoplasm, was relatively less susceptible to moisture stress than the strain B. carinata-24i synthesized from B. oleracea cytoplasm. The contiibution of higher ability inherited from the B. nigra parent and higher water status inherited from the B. oleracea parent resulted in drought resistance of B. carinata-226. B. carinata-24\, synthesized from reciprocal cytoplasm was, however, not able to maintain the high water status and thus was vulnerable to moisture stress.
Net CO2 exchange (Rn), stomatal conductance (gj, intemal CO2 concentration (Q), and water-use efficiency (WUE) of aging leaves were measured at the beginning of the dry season in 18 species in a tropical deciduous forest in Guanacaste, Costa Rica. In selected trees, gas exchange of old leaves was also compared with that of young leaves, and stomatal responses to irradiation and dark were measured. Based on comparisons with published data, and gj declined more rapidly with leaf age in deciduous than in evergreen species. Whereas both senescence and drought were implicated as causes of these dechneš in the deciduous species, the relative importance of factors responsible for the smaller decreases in physiological activity of old leaves of the evergreen species was less obvious. In the latter trees, and WUE of aging leaves, although not always as high as in young leaves, were high enough to refiite the suggestion that old leaves are solely a liability to tropical deciduous forest trees. On the other hand, stomatal closure in the dark was incomplete, potentially allowing water loss at night and during droughts.
Tolerance of Festuca rupicola Heuff., Botriochloa ischaemum (L.) Keng., and Salvia nemorosa L. to co-occurring drought, high air temperature and high irradiance were investigated in stands representing different degree of degradation. Air and leaf temperatures were higher for the stands in the advanced degradation stage. The net photosynthetic rate was not significantly lower and WUE was depressed in the degraded stands as compared to the intact stands. Carbon fixation type seems to have outstanding importance in the outcome of degradation processes in semiarid temperate grasslands.
In the dimorphic stag’s hom fem, Platycerium coronarium (Koenig ex Mueller) Desv., photosynthetic characters and chlorophyll (Chl) contents were deteiinined in both nést and pendulous fronds at different stages of ontogeny and at different positions along the longest length of each frond. Area-specific radiant energy- saturated net photosynthetic (P^) and dark respiration rates, dry mass-specific Chl content and quantum yield increased during frond development and decreased when senescence set in. Radiant energy-saturated and dry-mass specific Chl content were greatest in the youngest tissues of each frond. In addition to the functions ascribed to the nést (water and nutrient collection) and pendulous (reproduction) fronds, the results indicate the important roles of both frond types in providing Chemical energy to the growth and survival of the plant.
Comparison of 18 trees from three different stands of damage classes 0 ( healthy) to 3 (severely damaged) showed that die fimction of tfae photosynthetic apparatus measured either as the cUorophyll fluorescence or as the whole chain electron transport capacity remained staÚe. Only in springtime we could detect a decrease of photosynthetic activities in the most damaged trees. Nevertheless, flie synthesis of the D-1 reaction centre polypeptide increased with the degree of damage when measured as incorporation of i^C-leucine. Comparison with the content of Úie D-1 protein determined by immunoblotting showed that also the degradation of this protein was stimulated. This led to a strongly variable content of tfae D-1 protein in tfae damaged spruce trees. The content of tfae D-1 protein in faealthy trees was more or less constant. During springtime the degradation seemed to outbalance tfae syntfaesis in the damaged trees and the content of tfae D-1 protein was decreasing togetfaer with the photosynthetic activities. Hence the repair of the photosynthetic apparatus is enhanced in the damaged trees to keep the photosynthetic activities constant.
In field grown cashew trees {Anacardium occidentale L.) net photosynthetic rate (Pn) was maximum in leaves grown in all four directions (East - E, West - W, South - S and North - N) between 11 to 12 h. Between 15 to 16 h, photosynthetically active radiation (PAR) and were higher in W than in other directions, however stomatal conductance (g^) and transpiration rate (E) were similar in all the four directions. Maximum was found in the leaves of middle portion of the tree. Irradiance was more important for than gs, intercellular CO2 (Q), and E which did not exeit significant differences at different directions and timings.