High-temperature-induced Electrolyte Leakage from Excised Leaves and Roots of Three Hollies

Abstract

<jats:p>Membrane thermostability of `Needlepoint' Chinese holly (Ilex <jats:italic>cornuta</jats:italic> Lindl. &amp; Paxt.), `Albo-marginata' English holly <jats:italic>(Ilex aquifolium</jats:italic> L.), and `Nellie R. Stevens', an Ilex <jats:italic>aquifolium ×</jats:italic> Ilex <jats:italic>cornuta</jats:italic> hybrid, was determined by measuring electrolyte leakage in excised leaves and roots. The critical midpoint heat-killing temperature (T,) after a 30-min exposure was 54.4 ± 0.4C for `Nellie R. Stevens' leaves and was ≈ lC higher than that for Chinese (52.9 ± 0.3C) or English holly (52.9 ± 0.4C). The T<jats:sub>m</jats:sub> for English holly roots (53.9 ±_ 1.5C) was higher than that for either `Nellie R. Stevens' (51.7 ± 0.3C) or Chinese holly (50.1 ± 0.3C). The results of this study suggest that English holly and `Nellie R. Stevens' leaves and roots can withstand direct heat injury equal to or greater than that of Chinese holly.</jats:p>

Heat damage in boxed white spruce (Picea glauca [Moench.] Voss) seedlings: Its pre-planting detection and effect on field performance

“…5A) while a linear regression fit the data less well (y = -45.7 + 147 .67x, r2 = 0.92, MSE = 68 .287) (not shown) . The sigmoidal response curve we found to fit best is also described as typical for direct membrane injury due to heat stress (Blum and Albercon 1981 ;Ruter 1993 The relatively smaller amount of electrolytes released from needles compared to the stem sections may have been due to ion efflux being restricted only to the smaller diameter cut ends of the needle segments . However, the difference cannot entirely be due to physical means because stem segments also showed a greater sensitivity of response to the treatments, although variation was also greater.…”

“…Physiological testing of seedlings exposed to temperature treatments a) Electrolyte leakage from stem and needle segments An increase in electrolyte leakage from cells is evidence of excessive stress to tissues, and is considered one of the first signs of direct injury to cell membranes (Levitt 1980 ;Tal and Shannon 1983 ;Ruter 1993) . With conifers electrolyte leakage has been used to detect freezing stress (Burr et al .…”

“…1990;Sutinen et al . 1992) was used as an indicator of heat stress based on the assumption that a relationship exists between cellular membrane damage resulting from heat stress, and electrolyte efflux (Blum and Ebercon 1981 ;Tal and Shannon 1983 ;Ruter 1993 ;Burr et al . 1993).…”

“…The membrane thermal break-point (i.e . direct killing) for these seedlings appears to be 10 minutes at 52 °C (see also Ruter (1993) using different varieties of holly) . Indirect heat injury is observed after exposure to lower temperatures than those causing direct injury but is not apparent for many days or longer (Treshow 1970) .…”

“…They attribute the differences they found to the degree of saturation of fatty acids in the phospholipids of the cell membranes . Ruter (1993) used the method to show the membrane thermostability in holly was exceeded at >50 °C for 30 mins . This was attributed to loss of cell compartmentalization as a result of irreversible plasma membrane damage .…”