Cavitation studies on whole Ricinus plants by acoustic detection.

Acoustic detection has been used to investigate the incidence of cavitation in whole potted Ricinus plants subjected to water stress by withholding water. Cavitation proceeded rather slowly and was detectable before and during wilting. Techniques which restricted water uptake more drastically such as root cooling or overlapping cuts induced more rapid "click" production and wilting; a response already described for excised leaves. When water stress was removed by rewatering, or rewarming a cooled root system, cavitation soon ceased. This response was more sluggish of over-delayed.Cavitation in aging leaves on well watered plants has also been examined. Despite the onset of senescence over many days there was no evidence that dry patches, which often develop extensively, are a consequence of water shortage induced by xylem blockage. Leaves, falling naturally by abscission in still air, were often remarkably turgid with water potentials similar to those of healthy attached leaves. Only after losing water was cavitation apparent, as usual for excised mature leaves. Sometimes more persistent leaves did cavitate in situ, just before abscission, showing that in normal leaves xylem blockage can occasionally precede leaf fall by several hours.