White Dew: Flock of birds gather grain

March 20th, 2012
by Jo Law

Liza Dalby’s East Wind Melts the Ice tells us that this pentad marks the harvest season. The above-average rainfall, the associated widespread flooding and the reduced sunshine on Australian eastern seaboard have adversely affected many food crops. ABC Rural News reports: ‘Rain a pain for cane’ in northern Queensland and ‘Flood squeeze grape prices’ in the Riverina. The heavy rain is also delaying the annual harvest of Sydney rock oysters in New South Wales. Conversely, however, the wet weather has been good for the sowing of winter grains in South Australia.

Sadly, the wet condition has also resulted in a poor harvest for us in Austinmer. The tomatoes continue to put out lush dark green foliage but little fruit. What little fruits the plants bear remain green. The development of figs are somewhat held back by sudden leaf-drop (due to fungus). The passionfruit although ripe and plentiful are very sour. Only the cucumbers relish in the rain.

The ripening of fruit is triggered by the plant hormone, ethylene. The presence of this ordourless gas signals the production of enzymes in the fruit that in turn neutralise the acids, convert stratch into sugars, break down chlorophyll, and change large organic molecules into smaller, volatiles ones that we can smell. The enzymes pectinase and pectinesterase cause the pectin, a complex polysaccharide within cell walls that makes the unripe fruit hard, to degrade. Consequently, the bonds bewteen cells loosen and the fruit softens.

According to Ross Koning, whose fanscinating and detailed account informed my summary above, a similar process takes place when leaves fall off dedicious trees in autumn. Cooler night time temperatures together with the lessening of daylight provide the cue for the production of ethylene. Again, the enzyme hydrolase breaks down the chlorophyll in the leaf; the enzyme pectinase releases the bond between the layers of cells in the abscission zone (between the stem and the stalk) and the leaf falls. Ross Koning also deplores the eating of unripe pears. He strongly advises us to place the unripe fruit in a paper bag with a banana, which readily releases ethylene. In a few days, he says, we will be able to savour the delectable taste of a ripe pear.

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