V. S. Rama Das

Enhanced Rubber Accumulation and Rubber Transferase Activity in Guayule Under Water Stress

Summary Effects of water stress on rubber accumulation and on the activities of rubber transferase (Cis-1,4-polyisoprenyl transferase) were investigated in field-grown guayule ( Parthenium argentatum Gray) plants. A pronounced increase in the activities of rubber transferase was recorded in the stressed plants. An increase in enzyme activity was observed with decreased leaf water potential (ψ) from -0.5 MPa to -2.5 MPa and the activity declined thereafter. The rubber yield (per individual plant and on a per cent dry weight basis) also increased with a decrease in ψ value upto -2.5 MPa, followed by a sharp decline. Rewatering of the guayule plants increased the ψ value, followed by a continuous decline in the transferase activity over the next 9 days. The results indicate that maintainance of low leaf water potentials is advantageous for maximized rubber accumulation in guayule. The increased levels of rubber transferase activity during water stress were attributed to a shift in de novo synthesis of the enzyme, resulting altered patterns of rubber accumulation in guayule. The results point to a clear correlation between the ability of guayule to grow in arid areas and its better performance in rubber accumulation under controlled water-stress conditions.

Diversity in the Arrangements of Mesophyll Cells among Leaves of Certain C4 Dicotyledons in Relation to C4 Physiology

Summary A typical dorsi-ventral leaf anatomy with no evidence for radial arrangement of mesophyll cells around the prominent Kranz sheath, except in Portulaca oleracea and Trianthema portulacastrum, was observed in many C4 dicotyledons. Presence of one or two layers of colorless cells above the lower epidermis was a constant feature in most species. The plants possessed low CO2 compensation points and high rates of photosynthesis. C4 dicarboxylic acids, aspartate and malate, were the initial products of 14CO2 fixation. Phloem transport of assimilates was independent of photosynthetic rates. A negative correlation between leaf thickness and photosynthesis, transpiration and photosynthesis was observed. The mesophyll cells also showed, in some species, certain degree of staining for starch. The results were discussed and the necessity for re-evaluating the current schemes in relating the conventional Kranz anatomy with C4 physiology was suggested.

The Decarboxylating Systems in Fourteen Taxa Exhibiting CAM Pathway

Summary Fourteen taxa exhibited the characteristics of CAM pathway. Bryophyllum tubiflorum, Bryophyllum calycinum, Bryophyllum crenatum, Agave americana, Opuntia coccinellifera, and Sansevieria roxburghiana contained significant activities of NADP-malic enzyme. Euphorbia neriifolia, Euphorbia tirucalli, Euphorbia trigona, Pedilanthus tithymaloids, Polianthes tuberosa, Aloe vera and Cissus quadrangularis possessed higher activities of PEP-carboxykinase whereas the three species of Bryophyllum had substantial quantities of both NADP and NAD-malic enzyme. The results were discussed in relation to the mechanism of the operation of CAM pathway.

Biomass production of two species of Cleome exhibiting C3 and C4 photosynthesis

Abstract Striking interspecific differences in the net biomass production between the field grown Cleome gynandra L. ( Gynandropsis gynandra L.), a C 4 plant, and the C 3 species, Cleome viscosa L., were observed. Cleome gynandra possessed characteristically faster initial growth rate, and leaf area development attained its maximal growth much sooner compared to the C 3 species. The greater net biomass production and leaf area development of C. gynandra were correlated with quicker morphological development and the completion of the life cycle. It is believed that the advantage of the rapid initial growth in C. gynandra can be associated with a significant shortening of the duration of the life cycle.

C4 photosynthesis and a unique type of Kranz anatomy inGlossocordia boswallaea (Asteraceae)

A special form of Kranz anatomy, a single chlorenchymatous bundle sheath around a central ground tissue embedding the vascular bundles, was observed to be associated with the C4 pathway of photosynthesis inGlossocordia boswallaea, a member of Asteraceae. The chloroplasts were centripetally located in the sheath cells. During short term carbon fixation, C4 acids, aspartate and malate were predominantly labelled. Radioactivity was transferred from aspartate to sugar phosphates, sucrose and starchvia phosphoglyceric acid. Enzyme activities in the leaves revealed that the plant is an aspartate forming NAD malic enzyme type. The activities of both photosystems I and II were detected in mesophyll as well as the bundle sheath chloroplasts. The findings are discussed in relation to its tropical habitat.

Stomatal behaviour towards four classes of herbicides as a basis of selectivity to certain weeds and crop plants

Changes in the stomatal aperture and the rate of transpiration under foliar application with triazine (atrazine) urea (diuron), amide (alachlor, butachlor) and thiocarbamate (EPTC and Molinate) type of herbicides onAmaranthus viridis L.;Digera arvensis Forsk;Boerhaavia diffusa L.;B. repanda Willd.;Commelina benghalensis L.;Cyperus rotundus L.;Pisum sativum L.; andPennisetum typhoides Stapf and Hubb; were studied. It was observed that the triazine and urea herbicides have caused an appreciable stimulation of stomatal opening within two hours of chemical contact, while the amides possessed a contrasting behaviour in as much as they have brought a rapid closure of the open stomata. Thiocarbamates on the other hand have exhibited a differential response characteristically relating to the C3 or C4 type plants. The general trend observed with the thiocarbamates was that they were stimulatory for the C3 and inhibitory for the C4 plants in respect of stomatal opening.A definite correlation of the rate of the transpiration with the stomatal response to the herbicide was found. The present study suggests that the resistance or susceptibility of the plants is determined by the selective stomatal behaviour towards different herbicides.

INTERSPECIFIC DIFFERENCES IN THE CONSTITUENTS OF ESSENTIAL OILS OF CYMBOPOGON

Gas chromatography of essential oils ofCymbopogon showed striking interspecific differences in their major constituents. The two species of lemongrass,C. flexuosus andC. pendulus contained large amounts of citral while the citronella grass species,C. nardus andC. winterianus showed comparable amounts of geraniol, citronellal and citronellol. The essential oil ofC. martini was composed only of geraniol and citronellol and was therefore quite different to the other species. The gas chromatography profiles enable the identification of various species yielding essential oils characterised by their specific constituents.

Photosystem I Particles from Sorghum: Isolation and Characterisation of Chlorophyll-Protein Complexes under Differing Growth Light Regimes

Photosystem I (PS I) particles were isolated from sorghum thylakoids by Triton-X-100 solubilisation. The purified photosystem I particles possessed a chlorophyll/P700 ratio of 180 and a chlorophyll a/b ratio of 10. The polypeptide composition of the isolated PS I complex revealed a dominant 68kD polypeptide, four polypeptides in the range of 18–25kD associated with LHC-I and six minor polypeptides in the range of 8–24kD. The chlorophyll-protein (chl-protein) complexes of PS I were isolated from the purified particles by centrifugation in SDS sucrose density gradients. The complexes were designated as CP I, CP Ia and LHC-I. Sucrose density gradient ultracentrifugation resulted in two chlorophyll protein complexes associated with LHC-I-730 which were identified by their fluorescence emission spectra.

Leaf proteinase and nitrate reductase activities in relation to grain protein levels and grain yield in four species of grain amaranth

The relationship of leaf nitrate reductase (nr) and proteinase activities to the grain protein level and grain yield was investigated in four species of grain amaranth (Amaranthus hypochondriacus, A. caudatus, A. cruentus andA. edulis). A strikingly positive correlation between the leaf proteinase activity and the grain protein content was found.A. edulis with higher grain protein level possessed high leaf proteinase activity, whileA. hypochondriacus, with relatively lower grain protein content had lower leaf proteinase levels. Although there was no definite correlation between the leaf proteinase levels and the grain yield, the integrated leafnr activity was positively correlated with the grain yield. The total nitrogen content per plant seems to be dependent on the extent of root growth and the levels ofnr activity in leaves.

Isolation of intact mesophyll cells from the leaves of higher plants

A total of 146 species of angiosperms belonging to 35 taxonomically diverse families were screened for the isolation of living mesophyll cells from the leaves. Seventy-three species belonging to 22 families, on mild maceration in mortar with the isolation medium (pH 5·8) containing 0·7 M mannitoJ, 2 mM EDTA, 5 mM MgCl2, 5 mM K2HPO4 and 1 mM NaNO3, followed by fractional centrifugation, yielded intact mesophyll cells as seen under a research microscope. The high frequency of cell release, associated with the high percentage recovery of chlorophyll in cells was a common feature of most of the plant species examined by us. Nearly 87% of the chlorophyll present in the leaf could be recovered from the isolated cells inDolichos lablab. The isolated cells retained active photosynthetic carbon metabolism as evidenced by high rates of ferricyanide reduction as well as carbon assimilation.