Lactuca sativa cv. Outredgeous was grown under either fluorescent lamps or light-emitting diodes (LEDs) to test the hypothesis that antioxidant potential could be regulated by light quality. Red leaf lettuce was grown at 300 μmol·m−2·s−1 of photosynthetically active radiation, 1200 μmol·mol−1 CO2, 23 °C, and an 18 h-light /6-h dark photoperiod in controlled-environment chambers. The LED treatments were selected to provide different amounts of red (640 nm), blue (440 nm), green (530 nm), and far-red (730 nm) light in the spectra. Total anthocyanin content and the oxygen radical absorbance capacity of the tissue were measured at harvest. The source of light had a dramatic effect on both plant growth and production of radioprotective compounds. LEDs resulted in 50% greater bioprotectant content per plant at the same light level over triphosphor fluorescent lamps. Blue LEDs (440 nm) appeared to regulate the metabolic pathways leading to increased concentration of bioprotective compounds in leaf tissue. LED lighting induced a number of effects on morphology that increased both accumulation of bioprotective compounds and total yield.

The use of higher plants as the basis for a biological life support system that regenerates the atmosphere, purifies water, and produces food has been proposed for long duration space missions. The objective of these experiments was to determine what effects microgravity (microg) had on chloroplast development, carbohydrate metabolism and gene expression in developing leaves of Triticum aestivum L. cv. USU Apogee. Gravity naive wheat plants were sampled from a series of seven 21-day experiments conducted during Increment IV of the International Space Station. These samples were fixed in either 3% glutaraldehyde or RNAlater or frozen at -25 degrees C for subsequent analysis. In addition, leaf samples were collected from 24- and 14-day-old plants during the mission that were returned to Earth for analysis. Plants grown under identical light, temperature, relative humidity, photoperiod, CO(2), and planting density were used as ground controls. At the morphological level, there was little difference in the development of cells of wheat under microg conditions. Leaves developed in mug have thinner cross-sectional area than the 1g grown plants. Ultrastructurally, the chloroplasts of microg grown plants were more ovoid than those developed at 1g, and the thylakoid membranes had a trend to greater packing density. No differences were observed in the starch, soluble sugar, or lignin content of the leaves grown in microg or 1g conditions. Furthermore, no differences in gene expression were detected leaf samples collected at microg from 24-day-old leaves, suggesting that the spaceflight environment had minimal impact on wheat metabolism.

Intact apple (Malus domestica Borkh.) buds were examined by magnetic resonance imaging (MRI). MRI did not excite water in unchilled apple buds and could not image it. When chilling was satisfied, images were produced. We interpret this difference to mean that water is in bound and/or structured form in dormant apple leaf buds before the chilling requirement is satisfied. Conversion of bound to free water occurred equally in the low-chilling-requirement cultivar Anna and the high-chillingrequirement cultivar Northern Spy only after 600 and 4000 hours of chilling, respectively. It appears that processes involved in satisfying chilling requirement are also converting water in buds from bound to free form. Absence of free water in dormant buds during the winter signifies endodormancy, whereas when the water is in free form, buds are ecodormant. Thidiazuron, a dormancy-breaking agent, applied to partially chilled buds is instrumental in converting water to the free form within 24 hours. Summer-dormant buds contain free water, and they could be classified only as paradormant. Based on proton profiles, ecodormant and paradormant buds cannot be distinguished but endodormant buds can be readily identified.

Greenhouse grown 2-year-old potted `Jonathan' apple trees (Malus domestica Borkh.) were subjected to various levels of water stress in February. Midday leaf water potential (ψW), leaf osmotic potential (ψS), soluble sugars, and starch contents of mature leaves were measured throughout the development of water stress to determine whether active osmotic adjustment could be detected and whether carbohydrates were involved. Active adjustments of 0.6 MPa were observed 3 and 5 days, respectively, after water stress was initiated. Leaf turgor potential (ψP) could not be maintained through the osmotic adjustment when ψW dropped below -1.6 MPa. Sorbitol, glucose, and fructose concentrations increased while sucrose and starch levels decreased significantly as water stress developed, strongly suggesting that sugar alcohol and monosaccharide are the most important osmotica for adjustment. Sorbitol was a primary carbohydrate in the cell sap and accounted for > 50% of total osmotic adjustment. The partitioning of newly fixed W-labeled photosynthates in mature leaves was not affected by water stress immediately after the 30-min 14CO2 treatment. All the W-labeled carbohydrates decreased in the labeled leaves very rapidly after 14CO2 labeling. The decrease in 14C-sorbitol was greater than the decrease in other carbohydrates under both well-watered and stressed conditions. After 24 hours of water stress, however, the percentage of 14C-sorbitol increased while the percentages of sucrose, starch, glucose, and fructose decreased significantly with increasing levels of stress. The ratio of 14C-sorbitol in leaves with ψW = -3.5 MPa to leaves with ψW = -0.5 MPa was significantly higher than that of 14C-sucrose, 14C-glucose, W-fructose, or 14C-starch.

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