Optimal Reproductive Strategy of Plants, with Special Reference to the Modes of Reproductive Resource Allocation

Abstract A growth model for reproductive energy allocation pattern and schedule is proposed. Assumptions are as follows: (1) the assimilation rate for an individual is given by a logistic curve of vegetative dry weight; (2) size variability is expressed by the parameter W of the logistic curve (asymptotic value of vegetative dry weight); (3) a plant controls allocation of the assimilate to vegetative and reproductive structures so as to maximize the reproductive energy investment at the end of the growth period. The models were analyzed in comparison with field and experimental observations and gave reasonable explanations for the reproductive allocation pattern of individuals which reflects ecological preferences and life history characteristics, such as environmental conditions of habitats (stable or changing), length of life span (annual, biennial or perennial) and growth form (erectophile or planophile). Decreasing RA (reproductive allocation) with individual size and delayed switchover time from vegetative to reproductive growth were found in plants which occur in stable environments and have a more or less fixed growth period; in those which occur in changing environments where growth period depends on individual size, RAs that remain constant or increase with variations in individual size and early switchover time were detected. Most perennials conform to the former case, but annuals and biennials conform to the latter case. Under extremely overcrowded conditions, planophiles, which are much more subject to crowding effect than erectophiles, tend to have increasing RA with increasing size, while erectophiles tend to have almost constant RA irrespective of size. These trends are discussed in the light of the life history characteristics and ecological distribution of plant species studied.     

Sporophore Production in Sphaerobolus with Special Reference to Periodicity

Further observations on temperature and fruiting are reported.The minimum and optimum values depend on the time when observationsare made. The effect on discharge from sporulating culturesof illumination interrupted by dark periods (i-ii days) is considered.If the dark period does not exceed a day, harge recommenceson the second and subsequent days of renewed illumina if itis 2–4 days, discharge occurs on the second day afterreturn to light but not thereafter; if the period of darknessexceeds 5 days, discharge does not mmence on subsequent illuminationuntil a completely new crop of sporophores is formed. Experiments are reported in which it is shown that at 20°C there is an interval of about I day between the onset of adark period and the inhibition of discharge related to it. Thisperiod is increased to a day and a half at 10° C. At thistemper an alternation of roughly equal light and dark periodseach day leads to dis in the dark periods and not in the lightperiods as at 20° C. Experiments are reported which support the view that the long-termof discharge in cultures under constant conditions relates toinhibition of development of primordia by maturing sporophores.     

Correlation of Size of Dye Particle and Density of Substrate, with Special Reference to Mucin Staining

Phase contrast observations indicate that most mucins, and the perilacunar capsules of cartilage matrix, are of low refractive index and hence probably of low density. Mast cell granules and cell nuclei are somewhat more dense, but are rather variable. Cytoplasmic chromidial substance, nucleoli and the interstitial matrix of cartilage are of high density. The selectivity of alcian blue, dialysed iron, mucicarmine, mucihaematein and aldehyde fuchsin depends partly on these dyes being of large particle size (as shown by dialysis experiments); they are able to penetrate into and stain basophilic structures of low density (high “permeability” or “porosity”) but not into denser structures. Best's carmine also consists of large particles, and probably stains only those mucins which are of low density and which contain some strongly basic (acidophilic) groups.     

Effects of Canavanine on Arginine Utilization in Plants with Special Reference to Mitotic Activity

Excised primary roots of Phaseolus vulgaris L. were treated with canavanine and the effect on arginine utilization was studied. Arginine utilization was observed to be depressed to a low level by canavanine (1.8 × 10^?4M) in rapidly dividing and growing tissues. In addition, canavanine inhibited arginine utilization to a lesser degree in root sections composed of mature and non-dividing tissues. This demonstrated that canavanine inhibition is not limited to those tissues where active DNA synthesis occurs. Canavanine was observed to inhibit the onset of mitosis in primary roots as evidenced by a significant reduction of the frequency of mitotic figures. In addition, this amino acid was found to affect the course of mitosis once it was initiated by altering the relative frequency of mitotic stages, decreasing the percentage of prophase figures and increasing the percentage observed in the telophase. An influence on the rate of spiralization and despiralization of the chromosomes is suggested. The effects on mitosis are probably related to growth-inhibitory and toxic effects of canavanine. The possible function of canavine as an allelopathic substance is hypothesized.     

Nitrate Assimilation in Higher Plants with Special Reference to the Cocklebur (Xanthium pennsylvanicum Wallr.)

A soluble NADH-dependent nitrate reductase is described forthe shoot system of Xanthium. Young leaves and immature stemtissues contain high levels of the enzyme. They are relativelyrich in free amino acids and amides but store little free nitrate.The specific activity of the enzyme is lower in fully expandedleaves, although these leaves exhibit higher rates of fixationof carbon in photosynthesis than do younger leaves. Neithernitrate nor free amino acids accumulate in the mesophyll ofthe leaf. Older parts of the stem axis accumulate large amountsof soluble nitrogen, almost entirely as free nitrate. Reservesof nitrate in the shoot and root are rapidly depleted if nitrateis removed from the external medium. Nitrate reductase is apparently absent from roots of Xanthium.This finding is supported by analyses of bleeding sap from nitrate-fedplants which show that 95 per cent of the nitrogen exportedfrom roots is present as free nitrate. However, roots are capableof synthesizing and exporting large amounts of amino nitrogenif supplied with reduced nitrogen such as urea or ammonium. A scheme is presented summarizing the main features of the metabolismof nitrate in Xanthium and this is compared with the situationin nitrate-fed plants of the field pea (Pisum arvense L.), aspecies previously shown to be capable of reducing nitrate inits root system.