Gregory N. Brown

Chlorophyll fluorescence monitoring of freezing point exotherms in leaves

Abstract Following supercooling prompt chlorophyll fluorescence and delayed fluorescence from leaves undergo transients simultaneous with the freezing point exotherm. The degree of supercooling and, hence, the temperature at which the exotherm occurs is dependent upon the leaf water content. Winter wheat leaves ( Triticum aestivum L.) that had the lowest water content (hardened “Kharkov”) supercooled to a greater degree than those leaves with a higher water content (hardened “Rescue” and unhardened “Kharkov” or “Rescue”). Seeding the leaves with ice increased the temperature at which the exotherm occurred and decreased the difference between varities but not between hardened and unhardened material. Our results suggest that freeze-avoidance via supercooling may be one mechanism in winter wheat for withstanding subfreezing temperatures.

Ribonuclease activity during induction of cold hardiness in mimosa epicotyl and hypocotyl tissues

Abstract Ribonuclease activities in both epicotyl and hypocotyl tissues of Albizzia julibrissin seedlings decreased during induction of cold hardiness. Small decreases in fresh weights during induction of cold hardiness suggest a possible relationship between RNase activities and desiccation. Relative to increases in total protein during induction of cold hardiness, decreases in RNase activities suggest some degree of specificity, possibly invloved in regulation of RNAs and protein synthesis during induction of cold hardiness.

Xylem pressure potential and chlorophyll fluorescence as indicators of freezing survival in black locust and Western hemlock seedlings

Abstract Xylem pressure potential was determined using the Scholander pressure chamber on stems of cold hardened and non-hardened black locust ( Robinia pseudoacacia L.) seedlings following freezing to various nonlethal and lethal temperatures and subsequent thawing. Correlation was found between immediate xylem pressure potential and long-term seedling survival. Chlorophyll fluorescence transients were monitored using needles of western hemlock ( Tsuga heterophylla (Raf.) Sarg.) seedlings following freezing to various non-lethal and lethal temperatures and subsequent thawing. Immediate and repeatable differences in fluorescence transients correlated with long-term seedling survival. Methodology is described and correlations discussed relative to using either chlorophyll fluorescence or xylem pressure potential as an immediate indicator of long-term freezing survival in woody plant seedlings.

A solid-state device for the simultaneous measurement of prompt and delayed chlorophyll fluorescence induction transients in leaves☆

Abstract This paper describes a totally solid-state device designed to monitor simultaneously both prompt and delayed fluorescence transients in leaves. The light source is a filtered high intensity light emitting diode (LED) with a maximum usable output of 50 μE/m 2 /sec. The sensor consists of a very sensitive photo-diode-operational amplifier combination (9 × 10 7 V/W; 0.25-msec response time). Circuitry was designed to pulse the LED (0- to 25-msec pulse) and to intensify the trace monitored with a storage oscilloscope. The probe unit containing the emitter and sensor was designed so that the effects of different gas atmospheres and different temperatures could be studied. The effects of temperature on the performance of the device are described. Examples of simultaneous traces of prompt and delayed fluorescence are shown to indicate that good resolution of both phenomena can be obtained. To illustrate the utility of the device the low-temperature kinetics of prompt and delayed fluorescence of avocado ( Persea americana Mill.) are contrasted with the kinetics at room temperature.

Properties of chloroplast membrane-bound ferredoxin-NADP+ reductase during cold hardening of wheat. No indication of qualitative membrane changes during cold hardening

Kinetic parameters of the chloroplastbound ferredoxin-NADP+ reductase from two varieties of wheat (Triticum aestivum), hardy Kharkov 22 MC (winter wheat) and less hardy Rescue (spring wheat), were followed during induction of frost hardiness as a means of examining possible changes in chloroplast membranes during hardening. No changes were found in the Michaelis constants for NADPH and 2,6-dichlorophenol indophenol, inhibition constants for p-chloromercuriphenylsulfonate, and activation energy values of the enzyme in either variety. The data suggest that no qualitative changes occurred in the properties of wheat chloroplast membranes related to ferredoxin-NADP+ reductase during cold hardening.

A comparison of PPVT and SIT scores of young children

Eighty-four children from rural, urban, and suburban families were tested with the PPVT during a parent intervention program and with the SIT three years later as part of program evaluation. Results indicated the mean IQ on the SIT was substantially higher than expected based on the earlier PPVT scores. Sampling error and examiner error were excluded as explanations for the difference. These results suggest that the PPVT and SIT yield different scores and lack comparability.