Mark Rieger

Carbohydrate availability affects growth and metabolism in peach fruit

Along with sucrose, sorbitol represents the main photosynthetic product and form of translocated carbon in peach. This study aimed at determining whether peach fruit carbohydrate metabolism is affected by changes in source-sink balance, and specifically whether sorbitol or sucrose availability regulates fruit enzyme activities and growth. In various trials, different levels of assimilate availability to growing fruits were induced in vivo by varying crop load of entire trees, leaf : fruit ratio (L:F) of fruiting shoots, or by interrupting the phloem stream (girdling) to individual fruits. In vitro, fruit tissue was incubated in presence/absence of sorbitol and sucrose. Relative growth rate (RGR), enzyme activities and carbohydrates were measured at different fruit growth stages of various peach cultivars in different years. At stage III, high crop load induced higher acid invertase (AI, EC 3.2.1.26) activities and hexose : sucrose ratios. Both sorbitol and sucrose contents were proportional to L:F, while sorbitol dehydrogenase (SDH, EC 1.1.1.14) activity was the only enzyme activity directly related to L:F in both fruit growth stages. Girdling reduced fruit RGR and all major carbohydrates after 4 days and SDH activity already after 48 h, but it did not affect sucrose synthase (SS, EC 2.4.1.13), AI and neutral invertase (NI, EC 3.2.1.27). Fruit incubation in sorbitol for 24 h induced higher SDH activities than in buffer alone. In general, assimilate availability affected both sorbitol and sucrose metabolism in peach fruit, and sorbitol may function as a signal for modulating SDH activity. Under highly competitive conditions, AI activity may be enhanced by assimilate depletion, providing a mechanism to increase fruit sink strength by increasing hexose concentrations.

Reducing Yield Variation in Peach Orchards by Geographic Scattering

Assuming a declining correlation in yields as distance between pairs of orchards increases, yield variability in peach production may be reduced by increasing distances among orchards. As a measure of yield variability that avoids possible bias resulting from orchard-specific effects, a stochastic production function is estimated. Results support the assumption that a declining correlation between yields exists as distance increases. For every mile further apart, the correlation in yield declines 2.28%. Copyright 1997, Oxford University Press.

Flower orientation influences ovary temperature during frost in peach

Abstract Ovary temperatures of upward- and downward-facing flowers of ‘Junegold’ peach ( Prunus persica (L.) Batsch) were measured on five nights in March 1991 to determine whether differential survival of ovaries following frost was related to flower orientation. Flowering twigs were removed from mature trees and positioned horizontally approximately 1.5 m above ground level prior to occurrence of low temperatures (0–5°C). Thermocouples were inserted through the hypanthium to contact ovaries of upward- and downward-facing flowers, and temperature and meteorological data were logged every 5 min. Under clear, calm conditions, temperature of upward-facing flowers averaged 0.33°C lower than that of downward-facing flowers during the coldest period of the night, with maximal differences of 0.77°C. Under cloudy, calm conditions, temperature differences between upward- and downward-facing flowers were less frequently observed and lower in magnitude (0.08–0.15°C). Under windy conditions (> 2.5 m s −1 ), no temperature difference between upward- and downward-facing flowers occurred despite strongly negative net radiation. Differences in radiant heat exchange when forced convection was minimized are proposed to have caused the differential temperatures between flowers of different orientation. Based on known values of ovary cold tolerance, it is concluded that differences in survival of up to 38% could occur due to flower orientation when air temperature reaches critical values.

Mannitol-producing tobacco exposed to varying levels of water, light, temperature and paraquat

Summary Transgenic mannitol-producing (+mtlD) and wild-type (–mtlD) tobacco plants were exposed to water deficit, varying light intensities, low temperatures, and paraquat applications to test whether mannitol was involved in protection against abiotic stresses. In the water deficit experiment, –mtlD and +mtlD plants were fully irrigated [100% evapotranspiration (ET)] or received 25% ET for 40 d. Water deficit reduced the relative water content (RWC) of both types of plant, starting on day 22, and the total stem length (TSL) of –mtlD 25% ET plants after 11 d, whereas the TSL of +mtlD 25% ET plants was reduced only after 34 d. After 30 d of water deficit, a higher percentage of mature foliage was retained by +mtlD 25% ET plants compared to –mtlD 25% ET plants. The mannitol-1-phosphate dehydrogenase activity of +mtlD plants was not affected by water deficit. The photosynthetic rates of +mtlD and –mtlD plants were measured at PPFD levels ranging from 0 to >2,000 μmol m–2 s–1. No differences in quantum yield, saturation and compensation points, or dark respiration were observed between the +mtlD and –mtlD plants. Exposing the leaves of +mtlD and –mtlD plants to 0°C for 24 h caused significant injury to cell membranes and was similar in both types of plant. The application of 0.2 mM paraquat onto expanding –mtlD leaves produced a higher percentage of necrotic leaf area (4.3%) compared to +mtlD leaves (0.48%). The amount of mannitol produced by +mtlD plants could not provide significant osmotic protection, or increases in photosynthesis, whereas it may provide a specific system to protect cells from free radical-induced damage.

Development of a Distance Education Program by a Land-Grant University Augments the 2-Year to 4-Year STEM Pipeline and Increases Diversity in STEM

Although initial interest in science, technology, engineering and mathematics (STEM) is high, recruitment and retention remains a challenge, and some populations are disproportionately underrepresented in STEM fields. To address these challenges, the Microbiology and Cell Science Department in the College of Agricultural and Life Sciences at the University of Florida has developed an innovative 2+2 degree program. Typical 2+2 programs begin with a student earning an associate’s degree at a local community college and then transferring to a 4-year institution to complete a bachelor’s degree. However, many universities in the United States, particularly land-grant universities, are located in rural regions that are distantly located from their respective states’ highly populated urban centers. This geographical and cultural distance could be an impediment to recruiting otherwise highly qualified and diverse students. Here, a new model of a 2+2 program is described that uses distance education as the vehicle to bring a research-intensive university’s life sciences curriculum to students rather than the oft-tried model of a university attempting to recruit underrepresented minority students to its location. In this paradigm, community college graduates transfer into the Microbiology and Cell Science program as distance education students to complete their Bachelor of Science degree. The distance education students’ experiences are similar to the on-campus students’ experiences in that both groups of students take the same department courses taught by the same instructors, take required laboratory courses in a face-to-face format, take only proctored exams, and have the same availability to instructors. Data suggests that a hybrid online transfer program may be a viable approach to increasing STEM participation (as defined by enrollment) and diversity. This approach is particularly compelling as the distance education cohort has comparable grade point averages and retention rates compared to the corresponding on-campus transfer cohort.

Effect of cold and drought stress on blueberry dehydrin accumulation

Summary Dehydrins are a group of plant proteins which respond to any type of stress that causes dehydration at the cellular level, such as cold and drought stress. Previously, three dehydrins of 65, 60, and 14.kDa were identified as the predominant proteins present in cold acclimated blueberry (Vaccinium corymbosumLinn.) floral buds. Levels were shown to increase with cold acclimation and decrease with deacclimation and resumption of growth. In the present study, to determine if dehydrins are induced in other organs in response to low temperature treatment (48C) and in response to drought, accumulation of dehydrins was examined in leaves, stems, and roots of two cultivars and one wild selection (a V. corymbosum cultivar, a V. ashei Reade cultivar, and a V. darrowi Camp selection) of blueberry by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) followed by immunoblotting. Cold treatment involved placing plants in a cold room maintained at 48C for five weeks; drought stress was imposed by withholding water from potted, greenhouse-grown plants for 34.d. Relative water content (RWC) of shoots was determined periodically throughout the drought treatment. Dehydrins accumulated with both cold and drought stress but their molecular masses varied depending upon blueberry species. Dehydrins accumulated to higher levels in stems and roots than in leaves with cold stress and to higher levels in stems than in either roots or leaves with drought stress. Furthermore, cold treatment combined with dark treatment induced higher levels of dehydrins than cold treatment combined with a 10.h light/14.h dark photoperiod, suggesting that dehydrins may be responsive to changes in photoperiod as well. In the cold-stress experiment, the level of dehydrin accumulation was correlated with expected level of plant cold hardiness in the three genotypes. In the drought stress experiment, dehydrins accumulated prior to significant changes in RWC, and dehydrin levels did not appear to be closely correlated with RWC either among or within genotypes.