Dimitra A. Loka

High temperature limits in vivo pollen tube growth rates by altering diurnal carbohydrate balance in field-grown Gossypium hirsutum pistils

It has recently been reported that high temperature slows in vivo pollen tube growth rates in Gossypium hirsutum pistils under field conditions. Although numerous physical and biochemical pollen-pistil interactions are necessary for in vivo pollen tube growth to occur, studies investigating the influence of heat-induced changes in pistil biochemistry on in vivo pollen tube growth rates are lacking. We hypothesized that high temperature would alter diurnal pistil biochemistry and that pollen tube growth rates would be dependent upon the soluble carbohydrate content of the pistil during pollen tube growth. G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures but at the same developmental stage. Diurnal pistil measurements included carbohydrate balance, glutathione reductase (GR; EC 1.8.1.7), soluble protein, superoxide dismutase (SOD; EC 1.15.1.1), NADPH oxidase (NOX; EC 1.6.3.1), adenosine triphosphate (ATP), and water-soluble calcium. Soluble carbohydrate levels in cotton pistils were as much as 67.5% lower under high temperature conditions (34.6 °C maximum air temperature; August 4, 2009) than under cooler conditions (29.9 °C maximum air temperature; August 14, 2009). Regression analysis revealed that pollen tube growth rates were highly correlated with the soluble carbohydrate content of the pistil during pollen tube growth (r² = 0.932). Higher ambient temperature conditions on August 4 increased GR activity in the pistil only during periods not associated with in vivo pollen tube growth; pistil protein content declined earlier in the day under high temperatures; SOD and NOX were unaffected by either sample date or time of day; pistil ATP and water soluble calcium were unaffected by the warmer temperatures. We conclude that moderate heat stress significantly alters diurnal carbohydrate balance in the pistil and suggest that pollen tube growth rate through the style may be limited by soluble carbohydrate supply in the pistil.

The Physiology of Potassium in Crop Production

Abstract Potassium (K) plays a major role in the basic functions of plant growth and development. In addition, K is also involved in numerous physiological functions related to plant health and tolerance to biotic and abiotic stress. However, deficiencies occur widely resulting in poor growth, lost yield, and reduced fiber quality. This review describes the physiological functions of K and the role in stress relief and also provides some agronomic aspects of K requirements, diagnosis of soil and plant potassium status, and amelioration. The physiological processes described include enzymes and organic compound synthesis regulation, water relations and stomates, photosynthesis, transport, cell signaling, and plant response to drought stress, cold stress, salt stress, as well as biotic stresses.

Effects of high night temperatures on cotton leaf gas exchange and ATP levels at flowering.

Aims: To monitor the effects of high night temperatures on leaf photosynthesis and respiration, stomatal conductance and adenosine triphosphate (ATP) levels of cotton during its reproductive stage. Study Design: A two-factor factorial, the two factors being temperature and time (weeks), with 40 replications in each of the temperature treatment. Place and Duration of Study: Altheimer Laboratory, Department of Crop, Soil and Environmental Sciences, University of Arkansas, between September 2013 and June 2014. Methodology: Growth chamber experiments were conducted using cotton (Gossypium hisrsutum L.) cultivar ST5288B2F with the treatments consisting of normal day/night temperatures (32/24oC) and high night temperatures (32/30oC) for two weeks at flowering. Measurements of leaf photosynthesis, respiration, stomatal conductance and ATP levels were conducted in the end of the first and the second week after imposition of stress. Results: Leaf photosynthetic rates and stomatal conductance rates remained unaltered under higher night temperatures during both weeks of the experiment. In contrast, a significant increase in leaf respiration rates was observed at the end of the second week of the experiment with plants grown under conditions of high night temperatures increasing their respiration rates by 30% Original Research Article Loka and Oosterhuis; AJEA, 8(2): 99-106, 2015; Article no.AJEA.2015.152 100 compared to those grown under normal temperatures. Conversely, leaf ATP levels were significantly decreased under conditions of elevated night temperatures. Conclusion: It was concluded that higher than optimum temperatures during flowering had no significant effect on cotton leaf photosynthesis and stomatal conductance in contrast to leaf respiration and ATP levels that were significantly decreased.

How potassium deficiency alters flower bud retention on cotton (Gossypium hirsutum L.)

ABSTRACT Potassium (K) is fundamental for plant growth and development but despite the increased quantities of fertilizers applied, incidents of K deficiency are commonly observed. The objective of this study was to record the effects of K deficiency during cotton’s (Gossypium hirsutum L.) early reproductive stage on carbohydrate content and metabolism, total antioxidant capacity and oxidative damage of cotton flower buds as well as the physiology of the leaf, subtending to the flower buds. Growth chamber experiments were conducted using cotton cultivar DP0912 and treatments consisted of normal K and deficient K fertilization for the duration of the experiment. Potassium deficiency resulted in significant oxidative damage in the cotton flower buds, despite the substantial increase in their total antioxidant capacity. Sucrose metabolism of the flower buds was markedly affected resulting in significant reductions in all non-structural carbohydrate concentrations. Furthermore, K deficiency disturbed leaf physiology leading to increased membrane damage, decreases in chlorophyll and carotenoid content and ultimately leaf photosynthetic rates. Concomitant increases in specific leaf weight under K deficient conditions indicated reductions in photoassimilate translocation, which in conjunction with the disruptions observed in flower bud sucrose metabolism, due to the insufficient antioxidant response, resulted in significant decreases in flower bud retention.