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Amauri Alves Nery and Adonai Gimenez Calbo

Constant-pressure manometry, previously designed to study O2 and CO2 gas exchange in small pieces of tissue, cells, and organelles, was adapted to study bulky organs. According to this new procedure, a near-zero-volume Devaux chamber connects a manometer to the internal atmosphere volume (VG) of a plant organ covered by a layer of epoxy, submerged in unstirred water, kept at constant temperature, and kept at the same VG pressure. Equations, based on CO2 and O2 solubility at equilibrium with VG, were used to follow O2 consumption as a function of reduced internal O2 pressure over time [for organs with VG < 0.1 (v/v) and respiratory quotient (RQ) of 0.7 to 1.3] to observe the transition between aerobiosis and anaerobiosis and to measure CO2 evolution during the anaerobic phase. For those measurements, bulky-organ manometry performed consistently in tomato [VG = 6.41% (v/v)], sweetpotato [VG = 8.57% (v/v)], and potato [VG = 0.34% (v/v)]. The results indicate that constant-volume manometry is sufficiently precise to detect differences in respiratory metabolism as a function of intercellular O2 concentration in intact plant organs.

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Adonai Gimenez Calbo, Marcos David Ferreira and José Dalton Cruz Pessoa

A portable wiltmeter instrument to estimate leaf turgor pressure according to an adaptation of the flattening method was developed. In the instrument, a flexible inflating membrane presses the leaf against a flattening plate having small orifices surrounded by a finely engraved network of obtuse indentations through which air flow is delivered. During a measurement, as the compression builds up, the leaf is progressively molded against the flattening plate, and as a consequence, the air flow (x) crossing the plate is reduced toward zero. The smallest leaf compression (p0) that blocks the air passage is an estimate of the leaf turgor. Wiltmeter measurements were compared with pressure probe measurements of cell turgor pressure in detached leaves of lettuce (Lactuca sativa L.), kale (Brassica oleracea L. var. Acephala), and chicory (Chichorium endivia L.), which were allowed to suffer diverse levels of wilting caused by transpiration. Such observed wiltmeter readings were a little lower than the cell turgor pressure measured with a pressure probe; the regression coefficients between these methods were: 1.156 for lettuce, 1.13 for kale, and 1.036 for chicory. This portable quantitative procedure to measure leaf firmness has potentially valuable applications related to postharvest and field plant physiology studies.