Suzan E. Hetherington

PHOTOABATEMENT BY ANTHOCYANIN SHIELDS PHOTOSYNTHETIC SYSTEMS FROM LIGHT STRESS

Leaves and other chlorophyllous tissues of plants often show transient or permanent anthocyanin coloration. The question of whether anthocyanins can function as effective light screens to modulate photosynthesis in plants was addressed by comparing photosynthetic responses in reddish-purple pods with those in green pods of the ornamental leguminous tree Bauhinia variegata. For these comparisons the actinic radiation employed was either red radiation (RR) which was poorly absorbed by anthocyanin or blue-green radiation (BGR) which was strongly absorbed by anthocyanin. Photon yields of photosystem 2 (PS2) photochemistry and photochemical chlorophyll fluorescence quenching coefficients (qp), measured over a range of photon flux densities (PFD) up to 1200 µmol m-2 s-1 at 23 °C and at five temperatures from 8 to 28 °C at a PFD of 260 µmol m-2 s-1, were almost identical in green pods irradiated with either RR or BGR and in purple pods irradiated with RR. However, qp values remained much higher in purple pods irradiated with BGR, e.g., 0.80 in BGR versus 0.29 in RR at a PFD of 1200 µmol m-2 s-1 at 23 °C, and 0.67 in BGR versus 0.28 in RR at a PFD of 260 µmol m-2 s-1 at 8 °C. The higher values of qp in BGR compared to RR indicated that photoabatement by anthocyanin allowed the first stable acceptor of PS2, QA, to be kept in a more oxidized state, thus decreasing the likelihood of photoinhibition. This was confirmed by demonstrating a lower susceptibility to photoinhibition in purple pods than in green pods in the sunlight, either naturally in pods on trees or in detached pods exposed to photoinhibitory conditions. We conclude that photoabatement by anthocyanin is a mechanism for allowing maintenance of higher oxidative levels of PS2 acceptor during episodes of high radiation stress, thereby minimizing photodamage to photosynthetic tissues.

Postharvest heat disinfestation treatments of mango fruit

Postharvest heat disinfestation treatments have emerged over the past decade as viable non-chemical control methods for fruit flies in mango fruit around the world. The physiological responses of mango fruit both during and following a heat treatment determine the eventual eating quality of the fruit. This review describes the methods used to heat treat mango varieties for insect disinfestation. The physiological effects of heat treatments, particularly pretreatment conditioning and hot water treatments, on the fruit are covered in detail.

Effects of leaf: fruit ratios on fruit growth, mineral concentration and quality of mango (Mangifera indica L. cv. Kensington Pride)

SummaryTo determine the effects of leaf:fruit ratios on growth, mineral concentration and quality of fruit, 30 uniform ‘Kensington Pride’ mango trees had selected branches thinned to a single fruit and girdled to provide 30, 60 or 120 leaves per fruit. Control branches were not thinned or girdled and had on average 36 leaves per fruit. Decreasing the leaf:fruit ratio to 30 resulted in smaller fruit with lower dry matter (generally an indication of fruit maturity), but extended the number of days to the stage of eating-soft at 22·C (shelf life) by 2 d, increased pulp Ca concentrations, and improved storage performance by reducing external chilling injury. Increasing the leaf:fruit ratio to 60 produced larger fruit and extended shelf life by approximately 2 d, but had no effect on dry matter or pulp Ca concentrations. A further increase in the leaf:fruit ratio to 120 increased fruit size, dry matter and the severity and incidence of disease but had no effect on shelf life or pulp Ca concentrations. Girdling...

Boron deficiency of avocado. 1. Effects on pollen viability and fruit set

The effect of boron (B) supply on pollen viability was studied using Hass avocado trees (Persea americana) grown in a glasshouse pot experiment with B-deficient soil. Seven rates of B were applied to the soil 12 months prior to anthesis. The number of pollen grains germinating in an artificial minus-B pollen growth medium increased approximately 16-fold when B equivalent to 0.8 or 1.6 g m-2 was applied to the soil.

Micropropagated dwarf off-type Cavendish bananas (Musa spp., AAA) show improved tolerance to suboptimal temperatures

The responses of micropropagated normal plants and dwarf off-types of Cavendish (Musa spp. AAA) bananas to suboptimal temperatures were evaluated under field and controlled environmental conditions. Compared with bananas grown at 30/25 degrees C (day/night), leaf production at 18/14 degrees C was inhibited by 51% in normal plants and 18% in dwarf off-types. The emergence of the first leaf that developed at low temperature was delayed by 11 days for normal plants and 5 days for the dwarf off-types. Photoinhibition of lamina, measured by decrease in the chlorophyll fluorescence variable Fv/Fm, occurred in all banana plants growing in the field during the winter months. The extent to which the plants were photoinhibited was significantly greater for the normal plants than dwarf off-types. Under controlled environmental conditions, photoinhibition was similarly greater in normal plants than dwarf off-types. After 153 h at 18/14 degrees C and a 9-h photoperiod of photon flux density (PFD) of 380 mu mol/m(2).s, Fv/Fm was reduced by 22 and 13% for normal and dwarf off-types, respectively. When plants were exposed to 18 degrees C and a continuous PFD of 380 mu mol/m(2).s for 20 h, Fv/Fm was reduced by 50% for normal plants and 36% for dwarf off-types. The results of the study indicate that dwarf off-types generated from banana micropropagation showed improved tolerance to low temperature and light, showing better growth and lower susceptibility to low-temperature induced photoinhibition than normal plants.

Packaging to reduce water loss can delay ripening of mango (Mangifera indica L cv 'Kensington Pride') fruit

Summary. Water loss and premature ripening during postharvest handling reduce the market quality of mango fruit. Towards investigating the use of moisture barrier liners for mango fruit trays, relationships between in-package relative humidity and weight loss and ripening of ‘Kensington Pride’ fruit were studied. Individual fruit were held at 20°C in sealed plastic containers (small 1.2 L buckets). The lid of each container had a single circular hole. Holes were of various sizes, ranging from 5 to 135 mm diameter. Ripening mature green fruit held at the lowest relative humidity of 57% (135 mm diameter hole) lost weight at a significantly (P£0.05) greater rate (10 mg/g initial FW. day) than fruit at higher relative humidities of 59 (open air), 60 (95 mm diameter hole), 61 (55 mm diameter hole), 71 (35 mm diameter hole), 74 (25 mm diameter hole) and 83% (25 mm diameter hole plus free water). These fruit at higher relative humidities lost weight at rates ranging between 9 and 4 mg/g initial FW. day. Fruit softening and skin colouring rates were similar across all relative humidities. In a second experiment, mango fruit were allowed to ripen in containers with smaller holes, ranging from 5 to 95 mm diameter, in their lids. Fruit at the lowest relative humidity (60%, 95 mm diameter hole) lost weight at a significantly (P≤0.05) greater rate (9 mg/g initial FW. day) than fruit from other treatments. Furthermore, these fruit ripened about 2 days sooner than fruit at higher relative humidities: 85 (25 mm diameter hole), 88 (15 mm diameter hole), 91 (10 mm diameter hole) and 93% (5 mm diameter hole). Fruit at the higher relative humidities lost weight at rates between 6 and 2 mg/g initial FW. day, and ripened in 6 to 12 days. Thus, hole size can be varied in order to control in-package relative humidity and regulate mango fruit weight loss and ripening. Australian Journal of Experimental Agriculture, 1997, 37, 463–7 463

Loss of heat tolerance in ‘Kensington’ mango fruit following heat treatments

Abstract Conditions that promote loss of heat tolerance, or dehardening, of ‘Kensington’ mango fruit ( Mangifera indica Linn.) were investigated. Fruit were conditioned at 40°C for 8 h, and then placed at 22°C (dehardened) for 8, 16, 24 or 48 h prior to hot water treatment (HWT) (47°C held for 15 min). The greatest reduction in fruit heat tolerance occurred in fruit placed at 22°C for 16 h. Compared with the other conditioned fruit, these fruit had the highest incidence and severity of skin scalding, external cavities, starch layer, increased F 0 values and a lack of recovery in F V / F M ratios after HWT. It was concluded that the loss of heat tolerance in ‘Kensington’ fruit occurred at a slower rate than the increase in heat tolerance brought about by the 40°C conditioning treatments. Exposure of fruit to 22°C for 24 h or longer accelerated fruit ripening, and induced some protection against heat injury.

Boron deficiency of avocado. 2. Effects on fruit size and ripening

Soil boron (B) applications were made to avocados (Persea americana cv. Hass) growing on a low B Krasnozem soil with a clay loam texture. The B treatments had positive effects on fruit size and postharvest characteristics. Addition of B produced a 13–16% increase in average fruit size. Fruit harvested from control trees ripened earlier and had higher ethylene production at 20° C compared to +B trees. Days to eating softness and peak ethylene production were reduced by approx. 4.4 days in fruit from control trees.

Susceptibility of mango (Mangifera indica L.) to cold-induced photoinhibition and recovery at different temperatures

Cold-induced photoinhibition of photosynthesis and recovery from photoinhibition in mono- and poly-embryonic mango cultivars were investigated under field and controlled temperature and light conditions. Photoinhibition, measured as a decrease in the ratio of variable to maximum chlorophyll fluorescence emission (Fv/Fm), occurred in trees growing in the field in winter and early spring. Fv/Fm ratios of all cultivars began to decrease from about 0.49 in May, reaching minimum values of about 0.33 in mid July, and then gradually increased to around 0.68 and exceeded pre-winter values by early November. A seasonal change of leaf chlorophyll content in all cultivars followed a similar pattern to the changes in Fv/Fm ratios during winter. Susceptibility to cold-induced photoinhibition and a reduction in leaf chlorophyll content were greater in poly-embryonic cultivars than in mono-embryonic cultivars. There was a positive linear relationship between the minimum air temperature the night before the measurement and the leaf Fv/Fm ratio (r(2) = 0.62-0.70). In controlled environmental experiments, poly-embryonic cultivars were also more susceptible to photoinhibition than mono-embryonic cultivars. When held at 10 degrees C and irradiated with a photosynthetic photon flux (PPF) of 450 mu mol/m(2).s, photoinhibition in detached leaves increased linearly with time. The extent of the reduction in Fv/Fm ratios induced by 6 h irradiation was 43% and 56%, respectively, in mono- and poly-embryonic cultivars. Recovery from photoinhibition in detached leaves was promoted by exposure to a PPF of 20 mu mol/m(2).s for 24 h at 20 degrees C. Negligible recovery occurred in photoinhibited leaves maintained at 10 degrees C.

Cold-storage-induced changes in chlorophyll fluorescence of kangaroo paw Bush Dawn flowers

Effects on vase life and chlorophyll fluorescence were evaluated for kangaroo paw Bush Dawn flowers harvested from 3 growth environments and kept at 3 storage temperatures for 4 storage periods. Flowers were grown in a glasshouse, shadehouse and in the open. Harvested flowers were stored at 0, 7.5 or 13°C for 1, 2, 3 or 4 weeks. Minimum fluorescence values decreased progressively from 0.103 to 0.078 as storage temperatures increased from 0 to 13°C. Relative fluorescence ratios of stored kangaroo paw flowers were altered significantly in response to storage temperature, storage duration and growth environment. Relative fluorescence ratios decreased progressively from 0.778 to 0.649 with increasing storage duration from 1 to 4 weeks. Relative fluorescence values were 0.688, 0.784 and 0.711 for 0, 7.5 and 13°C storage temperatures, respectively. Minimum fluorescence did not differ among the growth environments, but relative fluorescence was highest for the shadehouse (0.760) and lowest for the open (0.695). Vase life was also influenced by storage temperature, storage duration and flower source. Main effect vase lives of flowers were 6.6, 7.2 and 3.4 days for 0, 7.5 and 13°C storage temperatures, respectively. Shorter vase life after storage at 0 than at 7.5°C indicates that Bush Dawn is chilling sensitive. Post-storage longevity of flowers from the shadehouse (6.5 days) and glasshouse (6.3 days) was greater than from the open (4.2 days). Relative fluorescence values, which decreased in a linear manner for all storage temperatures as storage duration increased, were significantly correlated with the vase life.