The role of sucrose synthase in the response of soybean nodules to drought

Experiments were carried out to investigate the effects of droughtstress on enzymatic activities related to carbon and nitrogenmetabolism in soybean nodules. Gradual drought stress, imposedby withholding water nutrients, resulted in declines in thewater potential of leaves and nodules consistent with a significantdecline in N2 fixation. However, the amounts of nitrogenasecomponents 1 and 2 were virtually unaffected by drought stress.Similarly, no significant changes could be detected in aspartateaminotransferase, phosphoenolpyruvate carboxylase, glutaminesynthetase or alkaline invertase activities throughout the experiment.In contrast, sucrose synthase (SS), one of the enzymes involvedin sucrose metabolism in legume nodules, declined dramaticallyin activity and in content within a few days of withholdingwater. Coincident with this decline in SS activity were significantincreases in the nodule contents of sucrose, total free aminoacids and ureides. The amounts of proline, however, did notincrease until some days later. It is suggested that SS mayplay a key role in the regulation of nodule carbon metabolismand, therefore, of nitrogen fixation under drought stress conditions. Key words: Glycine max, soybean, nodule metabolism, drought stress, sucrose synthase     

Papillar integrity as an indicator of stigmatic receptivity in kiwifruit (Actinidia deliciosa)

Stigmatic receptivity is a major factor limiting fruit set inkiwifruit (Actinidia deliciosa). The aim of this work was toknow what determines the cessation of stigmatic receptivityin this species. Stigmatic receptivity has been analysed inkiwifruit through the capacity of the stigma to sustain pollengermination and has been related to stigmatic development anddegeneration.The stigma of kiwifruit flowers has a papillatesurface which from anthesis is covered with an abundant exudate.Papillae are unicellular and contain a number of phenolic deposits.During the lifetime of the flower these papillae gradually loseturgidity, while stigmatic secretion increases until 5 d afteranthesis when papillae start rupturing and the papillar contentis liberated into the germination medium. Stigmatic receptivityis high at anthesis and lasts for the next 4 d. However, itdrastically decreases 5 d after anthesis and it is nil 2 d later.The pattern of stigmatic receptivity closely fits that of papillarintegrity, indicating that stigmatic receptivity relies on thisintegrity. Since papillar integrity can easily be evaluatedin stigmatic arms, this criterion can be used as a quick methodto estimate stigmatic receptivity. Key words: Actinidia deliciosa, kiwifruit, stigma, receptivity, pollen     

Estimations of mesozooplankton biomass in a coastal upwelling area off NW Spain

The abundance and several estimators of mesozooplankton biomass(dry weight, ash-free dry weight, displacement volume, carbonand nitrogen) were measured in a coastal upwelling area offLa Coru*****na (NW Spain) at monthly intervals between 1990and 1995. Holoplanktonic copepods dominated in most of the samples,but meroplanktonwere also important near the coast, especiallyduring late spring and through summer. Gelatinous organisms(medusae, siphonophores and larvaceans) reached significantabundances (-10%) in shelf waters by late summer, but also nearthe coast in spring. Log-linear equations were computed betweendry weight, displacement volumeand the other biomass estimators,to allow for interconversion among different measurements. Toprevent the influence of meroplankton and gelatinous zooplanktonin the estimations of biomass, the equations were adjusted usingonly samples in which the abundance of each of these groupswas <10% of total individuals. Our equations produced carbonand ash-free dry weight estimates that are comparable to thoseobtained with the ratiosgiven in other studies in the region.However, the esti mations of mesozooplankton carbon from displacementvolume using the adjusted equation with our data are lower thanthose reported previously for the area, which werecomputed usingequations adjusted with data from a different ecosystem. Theuse of interconversion factors taken from the literature isdiscussed, along with the implications of the estimations ofmesozooplankton biomass in the computations of the flux of carbonthrough the ecosystem.     

Particulate and dissolved phytoplankton production of the Patos Lagoon estuary, southern Brazil: comparison of methods and influencing factors

Uptake rates of ¹⁴C (filtration and the acidification-bubblingmethod—ABM) were measured weekly in a shallow region ofthe Patos Lagoon estuary (3207'S, 5206'W) between March 1989and March 1990. Phytoplankton production varied seasonally,the lowest values occurring in the austral winter (June–August1989) and the highest rates during spring and summer (March1989; September 1989–March 1990). Particulate carbon productionvaried between 0.65 and 70.6 mg C m^–3 h^–1 and wasmostly associated with organisms <20 µm (mean = 73.4%).Dissolved organic carbon (DOC) released by phytoplankton variedbetween 0.1 and 89.3 mg C m^–3 h^–1 representing     

Antioxidant Defences under Hyperoxygenic and Hyperosmotic Conditions in Leaves of Two Lines of Maize with Differential Sensitivity to Drought

The effects of hyperoxygenic and hyperosmotic stress on severalaspects of antioxidant defences were studied in the leaves ofa drought-sensitive (LG11) and a drought-tolerant (LIZA) lineof maize (Zea mays L.). When leaf disks were subjected to theseverest stress conditions (100% O₂ and 0.5 M mannitol), theactivities of antioxidant enzymes, such as superoxide dismutase(SOD), catalase (Cat), ascorbate peroxidase (Asc-Px) and glutathionereductase (GSSG-Red), remained higher in disks of LIZA thanin disks of LG11. The ratios of activities of SOD to Cat, SODto Asc-Px and SOD to GSSG-Red were much higher in leaf disksfrom LG11 than in those from LIZA. Damage, as indicated by,for example, the extend of lipid peroxidation, the destructionof chlorophyll and carotenoids, the decrease in levels of proteinsulfhydryl groups and the leakage of electrolytes from cellswas apparent in leaf disks of both LIZA and LG11 as consequenceof the applied stresses. However, the damage was less markedin LIZA than in LG11. (Received September 2, 1992; Accepted July 20, 1993)