Desiccation Tolerance of Papaver dubium L. Pollen during Its Development in the Anther

Abstract

Developing pollen of Papaver dubium L. becomes functional and desiccation tolerant at approximately 2 to 1 days prior to anthesis, coincident with degradation of starch and a doubling of the amount of sucrose, the primary soluble carbohydrate present. When anthers were taken from flower buds at 3 days before anthesis, pollen dehisced upon exposure to the ambient air. This dried pollen did not fluoresce with the vital stain fluorescein diacetate, had increased leakage of K , and did not swell properly in a germination medium. In contrast, pollen became functional and desiccation resistant when these young anthers were first incubated in a water-saturated atmosphere for 30 hours. Phospholipid composition revealed no major differences over the last 3 days of development. When this immature pollen was liberated mechanically and allowed to mature in humid air, starch degraded and sucrose content nearly doubled, and the grains became largely functional and dehydration tolerant. Large unilamellar vesicles were prepared from isolated phospholipids to study dehydration-induced fusion and leakage. When dried in the presence of increasing concentrations of sucrose, vesicle integrity was progressively retained. These data indicate that pollen maturation during the last 3 days of development occurred independently from the parent plant. Sucrose may play an essential role in the acquired tolerance to severe dehydration.Pollen and seeds are plant organs that are generally much more tolerant to dehydration, than are leaves and roots. Basic knowledge about this difference in drought tolerance is very limited, although acquisition of partial tolerance to desiccation has been extensively studied (for a review see Ref. 2). The primary focus of these studies is the behavior of membranes during drought stress, particularly the changes in composition of phospholipids as regulatory to the physical properties of the membrane, and the functioning of enzymes. There are several reports on the similarities between desiccation and freezing tolerance, in that exposure to desiccation stress improves tolerance for freezing (16,29).Sucrose levels have been found to increase during both cold hardening (1,24) and desiccation stress (2). After an initial attention to sucrose as a depressant of the freezing point, researchers lost interest because the elevated sucrose levels could not account for the considerable freezing tolerance found in coldhardened plants. However, isolated thylakoid membranes are protected from the adverse effects of freezing, desiccation and heat stress much better by raffinose and sucrose than by equimolal concentrations of glucose (24).In anhydrobiotic microscopic animals such as nematodes (20) and Artemia cysts (5), adapted to survive extreme desiccation, trehalose, the nonreducing disaccharide of glucose, is related to acquired tolerance to severe desiccation. Trehalose has been detected in a wide variety of anhydrobiotic organisms (7), but its presence in pollen of higher plants has not been reported (26). The st...

An Electron Paramagnetic Resonance Spin-Probe Study of Membrane-Permeability Changes with Seed Aging

“…Further lipid extraction and analyses were performed according to previously described methods (Hoekstra and van Roekel, 1988;Tetteroo et al, 1996).…”

Tolerance to environmental desiccation in moss sperm

“…Schonbek & Bewley, 1981;Oliver et al, 1997), and the ability to accumulate sugars during the latter stages of dehydration (e.g. Bewley et al, 1978;Hoekstra & Vanroekel, 1988;Koster & Leopold, 1988;Sun et al, 1994;Hoekstra et al, 2001).…”

Inter-Conversion of Carbohydrate Reserves from Pollen Maturation to Rehydration in a Chili Pepper

“…Because of that, the osmotic pressure caused by sucrose, and even glucose and fructose, would vary following the natural changes in water content along stages, then modifying the hydric relationship between pollen and the surrounding environment. The carbohydrate variations along the stages analyzed would evidence possible inter-conversions between the different substances quantified, considering that the pollen would be independent from the rest of the plant by 1 DBA [21], and no nutrients were added to the culture medium during rehydration. The increment of glucose and fructose towards maturation can be related to sucrose cleavage, and particularly to starch hydrolysis (glucose equilibrates with fructose via the hexose phosphate pool).…”