Photosynthesis and Stomatal Conductance of Potato Clones (Solanum tuberosum L.) : Comparative Differences in Diurnal Patterns, Response to Light Levels, and Assimilation through Upper and Lower Leaf Surfaces.

A few potato clones, such as A6948-4, had higher rates of photosynthesis in the field than the Russet Burbank and were able to maintain higher rates not only during mid-day but also in the early morning and late evening hours. In addition, they maintained higher carbon assimilation rates over a range of photosynthetic photon flux density from 400 to 2,000 microeinsteins per square meter per second.Stomatal conductance increased linearly as irradiance increased from 500 to 2,000 microeinsteins per square meter per second with all four potato clones that were examined. Obviously, comparative measurements of stomatal conductance or diffusive resistance with potato must be taken at a known and constant photosynthetic photon flux density.The upper (adaxial) leaf surface of some potato clones provided a surprising contribution to total carbon assimilation. Neither stomatal conductance, number of stomata per unit area, total area of the stomatal apparatus, nor chlorophyll content appear to account for differences in carbon assimilation rates among clones.

Pentose phosphate metabolism of potato tuber discs as influenced by prior storage temperature.

Tubers of Solanum tuberosum L. var. Russet Burbank, Kennebec, and Targhee were stored at 95% relative humidity and at 1.7, 4.4, 5.8, 7.2 or 10 C. Rates of O(2) consumption were measured periodically by removing individual tubers from storage, excising discs of pith parenchyma tissue, and incubating the discs in a Gilson respirometer at 30 C. With all three varieties, data suggest a greater involvement of pentose phosphate metabolism with tissues from tubers stored at 1.7 C as compared to those from higher temperatures. Discs from tubers stored at 1.7 C had higher respiratory quotient values (CO(2)/O(2)), were substantially less sensitive to the inhibitory effects of iodoacetic acid, and were somewhat more sensitive to the inhibitory effects of salicylhydroxamic acid than the discs from tubers stored at higher temperatures. Using [(14)C]glucose labeled in the 1 or the 6 carbon, mean C(1) to C(6) ratios in the Gilson after 3.5 hours of aging were 4.8:1 with discs from tubers stored at 1.7 C and 2.5:1 with discs from tubers stored at 7.2 C. Prior storage history is important in metabolic studies using potato tubers.

Abscission of Phaseolus and Impatiens Explants: Effects of Ionizing Radiation upon Endogenous Growth Regulators and de Novo Enzyme Synthesis.

Stem-petiole explants from the lower pulvinus of the primary leaves of Phaseolus vulgaris L. cv. Red Kidney and from Impatiens sultani Hook cv. Scarlet Baby were exposed to varying dosages of gamma-radiation. With bean, irradiation of 175 to 525 kiloroentgens (kR) significantly accelerated the onset of abscission with a maximum response at 175 to 280 kR. Higher dosages (beginning at 600-700 kR) usually prevented abscission. With Impatiens, 18 to 35 kR significantly accelerated both the onset of abscission and possibly the initial abscission rate; 350 kR cut the time to 100% abscission in half and substantially accelerated the initial abscission rate. Inhibition of abscission in Impatiens was not possible with the available dose rate (35 kR/hour).The accelerating effect of ionizing radiation was apparently due to primarily a reduction in auxin activity, thus accelerating the shift from the relatively ethylene-insensitive stage I to the ethylene-sensitive stage II. In vitro irradiation of exogenous auxin in agar substantially reduced the abscission-delaying effects of the auxin. The low dosage accelerating effects of the ionizing radiation were negated by exogenous auxin application, either prior to or following irradiation. With prior auxin application, a higher concentration of auxin was required to achieve the same delaying effects as with application following irradiation. Apparently due to this reduction in auxin activity, irradiation hastened sensitivity to exogenous ethylene.The accelerating effects of ionizing radiation may be secondarily due to increased levels of endogenous ethylene. With bean tissues, exposures of 262 through 1500 kR of gamma radiation increased the measurable levels of endogenous ethylene released into the ambient air within 2 or 3 days after irradiation.The results of actinomycin D treatment suggested that required de novo RNA synthesis occurred about 4 hours earlier in those Impatiens explants that had received 105 kR gamma radiation than in the nonirradiated controls.An increased mobilization of Ca from the abscission zone may be a contributing factor in the radiation-induced acceleration of abscission. For both bean and Impatiens, exogenous Ca inhibited abscission of irradiated and nonirradiated explants. In addition, a more concentrated Ca solution was required to inhibit abscission of irradiated bean explants, as compared to the nonirradiated controls.