Water Relations of Cacti During Desiccation: Distribution of Water in Tissues

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Abstract
Three species of cacti survived an average stem water loss of 81%. Fractional water loss was greater from water-storage tissue than from the chlorenchyma, as documented at the cellular level by determining changes in cell volume and at the tissue level by determining relative water content of chlorenchyma and storage tissues. For Carnegiea gigantea and Ferocactus acanthodes, this differential loss of water resulted from a decrease in the moles of solute per cell for storage tissue; hence, less water was retained at a given osmotic pressure than for the chlorenchyma. Opuntia basilaris lost less water from the chlorenchyma during drought because of a greater initial osmotic pressure in the chlorenchyma than in the storage tissue. Greater retention of water in the chlorenchyma would result in less disruption of photosynthetic activity in these cacti during drought.