Loss of green color (yellowing) in apples (Malus ×domestica Borkh.) is due to chlorophyll breakdown, an enzyme-mediated reaction conforming to first-order kinetics. Nondestructive measurements of yellowing, using a tristimulus chromameter, were related to chlorophyll content for `Cox's Orange Pippin' and `Granny Smith' apples stored at temperatures of 0 to 35 °C. Yellowing determined by rate constant (k) of total chlorophyll and changes in hue angle, as a function of temperature, increased slowly from 0 to 5 °C, increased exponentially from 5 to 20 °C, reached a maximum from 20 to 24 °C, then declined at higher temperatures. Values of k and the rate of change of hue angle were characterized by a modified Arrhenius equation. `Cox's Orange Pippin' apples harvested early had lower k and lower rates of hue angle change than late-harvested fruit. Values of k and hue angle change of `Granny Smith' apples differed between years but not between harvests. The method used to characterize the relationship between yellowing and temperature may describe changes in other important quality attributes of apple fruit during storage and shelf life and help evaluate the efficacy of cool-chain handling and storage systems.
Dry matter accumulation and partitioning in plants of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. (syn. Richardia pentlandii Wats.) were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. The relative rate of dry matter accumulation [relative growth rate (RGRM), g·g-1·d-1] was highly correlated with the partitioning of the daily increment of dry matter into leaf tissue [leaf matter partitioning (LMP), g·d-1 per g·d-1]. In contrast, a poor correlation existed between RGRM and net assimilation rate (NAR, g·m-2·d-1). Maximum values of RGRM increased linearly with increasing temperature (from 13 to 28 °C), with a base temperature of 2.1 ± 2.7 °C. The optimum temperature for growth was PPF dependent with maximum total plant dry mass occurring under high PPF (694 μmol·m-2·s-1) at 25 °C. However, as the plant responded to PPF by altering LMP, final total plant dry mass was actually greater under the low PPF regime (348 μmol·m-2·s-1) at temperatures <22 °C. The optimum temperature for dry matter accumulation was close to the average daily air temperature during the growing season for the natural habitat of the parent species. Similarly, the greater dry matter accumulation under the combination of either low PPF and cooler temperatures or high PPF and warmer temperatures was paralleled by the diversity of PPF habitats in the natural open grassland and forest margin the parent species occupies. It is therefore suggested that Zantedeschia `Best Gold' is well adapted to optimize growth under these environmental conditions.
Steady-state oxygen diffusion in flesh of apples (Malus domestics Borkh. cvs. Braeburn and Cox's Orange Pippin), Asian pears (Pyrus serotina Rehder. cvs. Hosui and Kosui), and nectarines [Prunus persica (L.) Batsch. cvs. Red Gold and Sunglo] was studied using a nondestructive method at 20C. Fruit flesh was found to exert a significant resistance to O2 diffusion resulting in measurable O2 gradients between tissues immediately beneath the skin and those at the fruit center for all these fruits. The magnitude of these O2 gradients varied between crops and cultivars and depended on the respiration rate and on effective O2 diffusivity in fruit flesh (De). Values of Dc varied with the cultivar and were broadly consistent with intercellular space volume. The range of De values obtained suggested that 02 diffusion in fruit flesh takes place in a combination of series and parallel modes in the intercellular space and fluid/solid matrix of the flesh. The results imply that O2 diffusivity in flesh tissues must be taken into consideration in the determination of critical external O2 level in controlled/modified atmosphere (CA/MA) storage.
Photosynthetic activity of individual leaves of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. [syn. Richardia pentlandii Wats.] (`Best Gold'), were quantified with leaf expansion and diurnally, under a range of temperature and photosynthetic photon flux (PPF) regimes. Predictive models incorporating PPF, day temperature, and percentage leaf area expansion accounted for 78% and 81% of variation in net photosynthetic rate (Pn) before, and postattainment of, 75% maximum leaf area, respectively. Minimal changes in Pn occurred during the photoperiod when environmental conditions were stable. Maximum Pn (10.9μmol·m-2·s-1 or 13.3 μmol·g-1·s-1) occurred for plants grown under high PPF (694 μmol·m-2·s-1) and day temperature (28 °C). Acclimation of Pn was less than complete, with any gain through a greater light-saturated photosynthetic rate (Pmax) at high PPF also resulting in a reduction in quantum yield. Similarly, any gain in acclimation through increased quantum yield under low PPF occurred concurrently with reduced Pmax. It was concluded that Zantedeschia `Best Gold' is a shade tolerant selection, adapted to optimize photosynthetic rate under the climate of its natural habitat, by not having obligate adaptation to sun or shade habitats.