Alfredo J. Huerta

Effects of sulfur nutrition on photosynthesis in cadmium‐treated barley seedlings

Abstract The effects of sulfur (S) nutrition at 0.1 or 1 mM S on cadmium (Cd) toxicity measured by photosynthesis in barley (Hordeum vulgare L. cv. UC 476) seedlings were studied. Eight‐day‐old seedlings were treated with 25 μM Cd by adding cadmium chloride (CdCl2) to the nutrient solution. Then photosynthetic carboxylation efficiency (ACi curve) and stomatal conductance of the primary and second leaves were measured at four and eight days after Cd treatment. Fluorescence parameters were measured every 24 h for eight days after two days of Cd treatment. At 20 days, plant growth parameters were measured and dry biomass determined. The results showed that ACi was significantly reduced by Cd, but more in the low (0.1 mM) S than in the high (1 mM) S‐treated plants. Stomatal conductance of plants was also decreased by Cd, but more in the low S‐treated plants. Low S‐treated plants exposed to Cd showed an increase in Fo and Fq, and a decrease in Fv/Fm and T1/2, indicating photoinhibitory damage to PSII. Analysis...

Exposure to environmentally relevant levels of cadmium primarily impacts transpiration in field-grown soybean.

Cadmium (Cd) is a toxic heavy metal released into agricultural settings primarily due to human activities. Cadmium is readily taken up by plants from the soil and has been shown to result in numerous changes to plant growth and physiology. In this study we examined the physiological effect of environmentally relevant levels of cadmium on field-grown soybean (Glycine max). No significant differences in carbon dioxide (CO2) assimilation response to leaf internal CO2 concentration, chlorophyll fluorescence, or growth parameters were observed. However, we did observe an increase in sap flow, a real-time measure of transpiration. Consistent with increased sap flow there was a significant increase in total daily sap flow and peak sap flow between the control and cadmium-treated plants. Our results suggest that treatment with environmentally relevant levels of cadmium primarily impacts transpiration.

Seasonal variation in photosynthesis and diel carbon balance under natural conditions in two Peperomia species that differ with respect to leaf anatomy1

Abstract The occurrence of crassulacean acid metabolism (CAM) and C3 photosynthetic activities in Peperomia species has been linked to the differential distribution of C3 and C4 photosynthetic enzymes within the distinct leaf tissue layers. Our objectives were to test if relative thickness of the spongy mesophyll layer is an indication of CAM and if the distribution of water in the leaf tissue changes in response to drought. Under field conditions we studied photosynthesis and water relations of Peperomia obtusifolia and P. macrostachya, species that differ in leaf anatomy. Gas exchange and titratable acidity were measured over a complete 24 hour photoperiod. Plant water status was determined at dawn while chlorophyll a fluorescence data were collected during the day (12 noon). Thickness of the distinct leaf layers was determined with the aid of a calibrated light microscope. Gas exchange and titratable acidity showed that when well-hydrated, P. obtusifolia has typical C3 activity and P. macrostachya has typical CAM activity with spongy mesophyll layer thickness of 26% and 76% respectively. With almost the same proportion of spongy layer, P. macrostachya was found to exhibit reduced CAM activity while P. obtusifolia switch from C3 to CAM during the dry season. During the dry season, P. macrostachya did not show significant change in leaf osmotic potential, whereas P. obtusifolia had a significant increase at dawn, likely due to malic accumulation. Relative water content (RWC) was reduced significantly for both species during the dry season with severe reduction in P. macrostachya. Though there was a drastic reduction in RWC, no change in thickness was noticed within the water storing hydrenchyma. This, in addition to reduced CAM activity, could be an adaptation by the plant to drought. We also found that the distribution of water in the leaf tissue changes in response to drought, from the hydrenchyma to the chlorenchyma in P. obtusifolia, but not the case in P. macrostachya. Chlorophyll a fluorescence parameters Fo and qN were significantly higher during the dry season for both species, in contrast to Fv/Fm and ΦPSII values, an indication of photoinhibition resulting from drought. Thus, under well watered and natural conditions, a thicker spongy mesophyll correlates with the presence of CAM in the species studied.

Leaf Growth and Canopy Development of Three Sugarcane Genotypes under High Temperature Rainfed Conditions in Northeastern Mexico

The aim of this study was to compare sugarcane (Saccharum spp.) canopy developmental components of three commercial varieties (CP 72-2086, Mex 79-431, and Mex 68-P-23) in a subtropical environment under rainfed and high temperature conditions, a poorly described topic in the literature. A field experiment was carried out in southern Tamaulipas, Mexico, throughout November 2011–January 2013 crop cycle, during which 111 of the days had daily maximum temperatures at or above 35°C. Number of leaves, leaf area, leaf appearance rate, and leaf area index (LAI) were determined. Thermal time exposure, °Cd (°C day−1), was determined based on total number of green ligulate leaves using 10°C as the base temperature. At 5000°Cd the number of leaves per plant ranged from 32 to 40 and the dependence of leaf emergence rate as a function of temperature was confirmed. The leaf emergence rate of CP 72-2086 was significantly greater than that of the other two varieties. Cultivars did not differ with respect to leaf length but differed for all other parameters measured. These results show the potential importance of considering sugarcane varietal differences in leaf phenology and canopy development for breeding programs focusing on rainfed and high temperature conditions.

Floral biology and the evolution of selfing in natural populations of Clarkia tembloriensis Vasek (Onagraceae)

Abstract Populations of wide-ranging plant species may vary significantly from one another with respect to physiological and reproductive traits, allowing each population to adapt to its local environment. One example of this variation is observed as differences in floral form and breeding system. In the California wildflower Clarkia tembloriensis Vasek, breeding system varies from populations of outcross-pollinating individuals, with relatively large, protandrous flowers, to populations of self-pollinating individuals, with small, nonprotandrous flowers. Variation within the selfing flower types includes populations with small flowers that are polymorphic for petal form; WT (flowers with normal expanded petals) and crinkle-petal (cp; flowers with small, unexpanded petals). The aims of this study were to investigate the nature of this variation in floral biology with respect to resource allocation to male and female function and to components important for reproductive success in the six California populations included in this study. Our study revealed that more resources were allocated to pollen production relative to ovule production in large, outcrossing flowers than in small, selfing flowers. Pollen deposition on the stigma was significantly higher in selfing flowers than it was in outcrossing flowers and significantly higher in cp selfing flowers than it was in WT selfing flowers. Despite these differences, sufficient pollen was deposited on stigmas in all populations to fertilize available ovules. The numbers of seeds produced per capsule was significantly lower in populations of C. tembloriensis, with small, selfing flowers than it was in large, outcrossing flowers, which was probably due to differences in rainfall amounts between populations. Large outcrossers occupy the core of the species range, whereas small selfers occupy marginal habitat. The differences we observed reflect adaptations of each population to their local environment.