C. F. Cresswell

The effect of nitrogen on the development and photosynthetic activity of digitaria eriantha steud. subsp. eriantha

Abstract Digitaria eriantha Steud. subsp. eriantha, plants were grown under controlled conditions and treated with different concentrations and forms of nitrogen. The plants showed a preference for nitrate nitrogen, as opposed to ammonium nitrogen, with greater total dry matter production and leaf areas being recorded. The effect was enhanced as the concentration of nitrate nitrogen was increased. Whole plant net photosynthetic rates appeared to vary according to the units in which the activity is expressed. The optimum levels of photosynthetic activity differed with the stage of development, depending on the basis of expression. The form and concentration of nitrogen applied influenced morphological development and flowering, a result that could have important economic implications.

The influence of nitrate and ammonia nitrogen on the photosynthetic and photorespiratory activity of selected highveld grasses exhibiting c‐4 photosynthesis

Abstract A study has been made on the influence of nitrate and ammonia nitrogen on the carbon dioxide compensation point (T), carboxylating enzymes and growth of highveld grasses found at the primary, secondary and climax successional stages. The results obtained are discussed in relation to the influence of nitrogen on grassland succession found on the highveld.

Variability in leaf surface features and water efficiency utilisation in C3 and C4 forms of alloteropsis semialata (R. Br.) hitchc.

Alloteropsis semialata (R. Br.) Hitchc. Occupies a unique position both taxonomically and physiologically in the Gramineae in that C3 and C4 photosynthetic and anatomical forms exist within a single taxonomic species. Both forms have been collected from a single ecological niche in the Transvaal highveld. This study shows further morphological and anatomical differences between the two forms with respect to stomatal size, and frequency of distribution, as well as differing epidermal cell characteristics. In addition physiological differences between the two forms are established with regard to photosynthetic rates, transpiration rates, and boundary layer and stomatal resistances. The C4 form was found to be more efficient with respect to water utilization efficiency. Keywords: alloteropsis semialata; botany; characteristics; distribution; grasses; leaves; photosynthetic rate; plant physiology; south africa; stomatal resistance; transpiration rate; transvaal highveld; water use efficiency; water utilization

The effect of night temperature and leaf inorganic nitrogen status on the C4 Pathway enzymes in selected C4 photosynthetic grasses

Abstract Themeda triandra, Hyparrhenia hirta and Zea mays have a single bundle sheath with agranal, centrifugal chloroplasts suggesting a NADP‐ME‐type photosynthetic pathway. Plants grown in liquid cultures had a higher NADP malic enzyme activity than those grown in sand with nutrients being supplied. Decreased minimum night temperature and infiltration of inorganic nitrogen ions appeared to affect the decarboxylating systems of these species suggesting that this pathway is variable under different environmental conditions. Results are discussed in relation to nomenclature of the three distinct anatomical and biochemical C4 photosynthetic types.

A stimulation of an alternative photorespiratory CO2 pathway by nitrogen in themeda triandra ‐ a possible explanation for its sensitivity to nitrogen

Abstract Vacuum infiltration of inorganic nitrogen ions affected the photosynthetic rate and CO2 compensation point of Themeda triandra and Zea mays in a similar way. However these two plants differed markedly in their photorespiratory mechanisms in response to inorganic nitrogen. Increased nitrogen levels in the in vitro reaction mixture stimulated T. triandra RuBP oxygenase activity (500%), but the similar enzyme from Z. mays showed no response to nitrogen. Using metabolic inhibitors it appears that glycolate and glyoxylate may serve as substrates for photorespiratory CO2, producing formate. T. triandra leaf formate levels increased considerably with infiltration of increased inorganic nitrogen levels. This was not the case in Z. mays. In T triandra an alternative photorespiratory pathway appears to be operating under high nitrogen: this pathway would utilize inorganic nitrogen more efficiently with a greater loss of photorespiratory CO2, resulting in decreased productivity. Z mays did not exhibit any o...

A study of the fine structure, enzyme activities and pattern of 14co2 incorporation of highveld grasses from different successional stages

A detailed study of selected grasses has been made with respect to fine structures characteristics, enzyme activities associated with C-4 and C-3 pathway photosynthesis, and short term carbon dioxide-14 incorporation experiments. A good correlation was obtained between the fine structure, the carbon pathway and the successional position of the grasses studied. Keywords: enzyme activities|patterns|highveld grasslands|grasses|successional stages|characteristics|C4 pathways|C3 pathways|photosynthesis|carbon dioxide|experiments|fine structures|carbon pathways|Transvaal|Highveld|Gauteng Province|compensation points

The effect of micronutrients and gibberellic acid on the germination and metabolism of seedlings of themeda triandra forsk

Abstract Dormancy of the caryopsis of Themeda triandra Forsk was shown to be broken by the addition oi boron to the germination media. This effect was specific to boron, as no response was observed with zinc, copper, manganese, iron, cobalt and molybdenum in the germinating media. Evidence is put forward suggesting that dormancy is regulated by the stale of the endogenous boron in the caryopsis. It was found to stimulate the synthesis of RNA in the embryo and endosperm tissue, and also α‐amylase activity in both tissues, particularly the endosperm. The transiocation of the sugars from the endosperm to the embryo appears also to be regulated by boron. Gibberellic acid was also found to break dormancy, and to stimulate RNA synthesis and α‐amylase activity in the caryopsis.

Growth analysis and photosynthetic rates in three selected grass species in the Burkea-eragrostis savanna

Abstract Three major grass species of the Nylsvley study site were studied: Eragrostis pallens. Digitaria eriantha and Panicum maximum. Growth analysis for the peak growth season was carried out with respect to phytomass, biomass and necromass. The results of this analysis were correlated to photosynthetic activity, measured using infra‐red gas analysis and labelled carbon dioxide leaf exposures. Detailed studies of driving force variables, such as light, temperature, soil moisture and leaf water potential were carried out in order to determine their effects on stomatal resistance. From this it is anticipated that it will be possible to estimate the increase in biomass and the factors determining it, throughout the growing season.

An ontogenetic study with special reference to leaf development in C3 and C4 forms of alloteropsis semialata

Abstract This ontogenetic study conducted at light and electron microscope level, describes several aspects of leaf development in C3 and C4 forms of Alloteropsis semialata. Emphasis is placed on the distribution and anatomy of vascular bundles as seen in transverse sections. The derivation of the specialized photosynthetic tissue of the Kranz sheath, which characterizes the C4 form, is traced in the inner or mestome layer of the double bundle sheath. The lamina and sheath in successive leaves of comparable age in the two forms were used. The proportion of photosynthetic tissue present in sections taken at midlamina is assessed quantitatively using a planimeter. The main conclusions drawn from this study are summarized as follows: 1. lamina and sheath in leaves of A. semialata, in common with other grasses, are derived from different meristems, show different patterns of vascularization and mature at different rates, the tip representing an older portion of the leaf than the base; 2. the differences in bu...

In vitro regeneration of Digitaria eriantha

Embryogenic callus was obtained from immature regions of the leaf of Digitaria eriantha when grown in the dark on a MS medium supplement with 1, 0 or 2, 0 mg/dm 3, 2, 4D and 3-9% sucrose. Plantlet regeneration occurred when the calli were transferred to MS medium containing 0, 1 mg/dm 3, 2, 4-D and 7-8% sucrose, and placed under 16 hour photoperiod. The regenerated plantlets were successfully planted out into a mixture of sand and potting soil. Keywords: 2, 4-d; botany; callus; digitaria eriantha; embryogenic callus; leaves; photoperiod; plantlets; regeneration; sucrose