Showing papers on "Plant physiology published in 1989"

Photosynthetic properties of leaves of a yellow green mutant of wheat compared to its wild type.

Abstract: We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O2 evolution of the leaf tissue in saturating light and CO2 was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO2 assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.

Recovery from photoinhibition: effect of light and inhibition of protein synthesis of 32-kD chloroplast protein.

Abstract: Recovery from photoinhibition of photosynthesis in intact Lemna gibba was studied in presence of the protein synthesis inhibitors chloramphenicol and cycloheximide. Exposure to an irradiance of 1000 μmol m(-2)s(-1) in N2 for 90 min induced 80% photoinhibition. The plants recovered photosynthesis when transfered to normal irradiances (210 μmol m(-2)s(-1)) and air. Chloramphenicol added to the medium was taken up by the plant and reduced photosynthesis slightly. Recovery from photoinhibition was more inhibited than photosynthesis. Cycloheximide was also taken up by the plants and reduced synthesis of light harvesting chlorophyll protein: however, neither photosynthesis nor recovery were much affected. Synthesis of 32-kD chloroplast protein during recovery was inhibited by chloramphenicol, but not by cycloheximide. Synthesis of 32-kD protein was enhanced by 20-210 μmol m(-2)s(-1) light. The results support the hypothesis that synthesis of 32-kD protein is important for recovery of photosynthesis after photoinhibition.

Gibberellin involvement in dormancy-break and germination of seeds of celery (Apium graveolens L.)

Abstract: The temperature-dependent, primary dormancy of cv. Florida 683 celery seeds in darkness was partially broken by a 30 min light exposure on the third day of incubation at 20–22°C, resulting in c 50 percent germination after 20 days. This light stimulation was negated by including different inhibitors of gibberellin biosynthesis in the incubation medium. Subsequent addition of a solution of the gibberellins A4 and A7 or of the gibberellin-active compound (1-3-chlorophthalimido)-cyclohexane carboxamide (AC94,377) overcame the inhibitory effects on germination of these GA-biosynthesis inhibitors. It is suggested that light stimulates the biosynthesis of gibberellins which are essential for dormancy-break in celery seeds and that this biosynthesis is either directly or indirectly controlled through phytochrome.

Reduction in chlorophyll content without a corresponding reduction in photosynthesis and carbon assimilation enzymes in yellow-green oil yellow mutants of maize.

Abstract: The photosynthetic properties of a yellow lethal mutant, Oy/oy, and two yellow-green mutants of maize which are allelic (a homozygous recessive oy/oy and a heterozygous dominant Oy/+) were examined. Although Oy/oy had little or no chlorophyll or capacity for CO2 fixation compared to normal siblings, it had 28% as much ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity, and from 40% to near normal activities of C4 cycle enzymes. Both yellow-green mutants had only half as much chlorophyll per leaf area as normal green seedlings in greenhouse-grown plants in winter and spring. However, the absorbance of light by the mutants was relatively high, as their transmittance was only 5 to 8% greater than normal leaves. In winter-grown greenhouse plants, the activities of Rubisco and several C4 cycle enzymes in the mutants were unaffected and similar to those of normal seedlings on a leaf area basis. After allowing for small differences in leaf absorbance, the light response curves for photosynthesis in the mutants were similar on a leaf area basis but much higher on a chlorophyll basis than those of the normal seedlings. In spring-grown greenhouse plants the enzyme activities and photosynthesis rates were about 30% lower per leaf area in the yellow-green mutant leaves compared to the wild type. The maximum carboxylation efficiency (measured under low CO2 and 1000 μmol quanta m-2 s-1) in the mutants and normal leaves was similar on a Rubisco protein basis. The results indicate that maize can undergo a 50% reduction in chlorophyll content without a corresponding reduction in enzymes of carbon assimilation, and still maintain a high capacity for photosynthesis.

Action of Fusicoccin in vivo: Physiological and Biochemical Consequences

Abstract: A large number of papers demonstrate the interest of fusicoccin (FC) for both plant physiology and plant pathology This interest is explained by the following observations: (1) FC induces a strong stimulation of active electrogenic H+ extrusion, a process of fundamental importance for solute uptake, transport at the cell level and translocation in the plant, (2) practically all plant tissues of practically all higher plant species respond to FC, (3) the promotion of electrogenic, active H+ extrusion by FC mimicks, on an enlarged scale, the similar effect of natural important hormones such as auxin and brassinolide, while it antagonizes that of abscisic acid, (4) FC strongly influences various important physiological functions, such as mineral nutrition, growth by cell enlargement, stomata aperture (thus transpiration and photosynthesis) and the breaking of seed dormancy, these effects being apparently consequences of that on H transport, (5) recent results point to conclude that the primary target of FC is located in the plasma membrane, and that all the metabolic and physiological effects of this toxin depend on its capacity to activate the H+ transporting ATPase directly at the plasma membrane

Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid in a long-day plant,Chenopodium murale L., as influenced by photoperiodic flower induction

Abstract: Chenopodium murale plants, induced to flower by 5 days of continuous light, produced 43% more ethylene than vegetative plants kept under short days (16 h darkness, 8 h light). The 1-aminocyclopropane-1-carboxylic acid (ACC)-induced ethylene production, using saturating ACC concentration (10 mol·m−3) was also 55% higher in induced plants. Their ACC and N-malonyl-ACC (MACC) levels were also higher, the former increasing by 56% in both shoots and roots, the latter by 288% and 108% in shoots and roots, respectively. Administration of labeled [2,3-14C]ACC produced a very similar relative content of ACC and MACC in both treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 66% more ACC than the vegetative ones. The effects of photoperiod on ethylene formation and metabolism in a long-day plant (LDP)C. murale and a short-day plant (SDP)C. rubrum are compared. Ethylene formation seems to be under photoperiodic control in both species, but its role in flower induction remains obscure.

Photosynthetic activity of chloroembryos of a few selected tropical plants

Abstract: The role of chlorophyll in the mature embryos of several tropical plants (Phthirusa pyrifolia [H.B.K.] Eichl. [Loranthaceae]. Murraya koenigia Kurz. [Rutaceae], Murraya paniculata Jack. [Rutaceae], Syzygium cuminii [L.] Skeels [Myrtaceae]) was investigated. Extracted chloroembryos of all species do photosynthesize when illuminated. Whole mature fruits of M. koeningii, M. paniculata and Syzygium cuminii exhibited some photosynthetic activity, but pericarps of none of the fruits photosynthesized when exposed to light. Thus the photosynthetic activity of fruits may be ascribed to CO2 uptake by chloroembryos embedded in the fruits. A specific aspect of plant physiology, namely the re-utilization of respired CO2 in the process of photosynthesis is emphasized. It is postulated that within embedded chloroembryos, conditions such as high CO2 concentration, high light intensity, and low oxygen concentration are favourable for conducting intensive photosynthesis. Photosynthesis within enclosed organs has an additional advantage in that is does not expose the plant to any risk of water loss usually associated with photosynthesis.