Water Loss via the Glandular Trichomes of Chickpea (Cicer arietinumL.)

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Abstract
During late vegetative growth chickpea leaves and stems can be covered with aqueous glandular droplets. If these droplets persist at low humidities there may be substantial water loss via the glandular trichomes Four solution culture experiments in growth chambers tested for glandular water loss at different humidities. In the daytime, exudate persisted between relative humidities of 55% and 95%, and the exudate water potential varied between - 2.0 M Pa and - 8.0 M Pa. Even by night, chickpea leaves, like wetted alfalfa leaves, were cooler than non-wetted alfalfa leaves or the ambient air. Daytime leaf temperatures were significantly higher in a mutant that produced fewer droplets than in its normal parent. It was concluded that water loss via the glandular trichomes can be enough to lower leaf temperature by several degrees C within a wide range of atmospheric conditions. The exudate solutes, analysed to confirm the osmotic potential measurements, were primarily malic, hydrochloric and oxalic acid. Without the strong acids a chickpea leaf, wet even on dry days, would be ripe for parasitic attack.