Extension Growth in Primary Cell Walls with Special Reference to Elodea canadensis

A quantitative study of distribution of perforations in thecellulose frame-work of longitudinal walls of cortical parenchymashows that their number and spacing change in an orderly manneras the tissue grow. These perforations are considered to bepit-fields, not primarily concerned with cell-wall growth, sincethey do nto occur in walls adjacent to intercellular spaces.The data are discussed in relation to the general problem ofcell extension, and are interpreted as showing that cell-wallgrowth is intersusceptive throughout; tip-growth does not occur.     

Endogenous Abscisic Acid Content Correlates with Photon Fluence Rate and Induced Leaf Morphology in Hippuris vulgaris

This research focused on studying how light and endogenous abscisic acid regulate leaf development in Hippuris vulgaris, a species of heterophyllic aquatic plant. Amounts of photosynthetically active radiation greater than 300 micromoles per square meter per second caused submerged H. vulgaris shoots to produce aerial-type leaves. Abscisic acid was not detected in shoots grown under noninducing light quantities (100 micromoles per square meter per second), but was present at 13.4 nanograms per gram fresh weight in shoot tips after plants were exposed to 1 photoperiod of inducing light (500 micromoles per square meter per second). This supports a role for abscisic acid in the high light-induced heterophylly in H. vulgaris, and provides additional support for the general hypothesis that abscisic acid regulates leaf development in heterophyllic aquatic plants. No relationship was observed here between postphotoperiodic light treatments of various red/far red ratios and heterophylly in H. vulgaris.     

Fruiting in Sphaerobolus with Special Reference to Light

Sphaerobolus grows and, provided there is sufficient illumination,fruits readily on oatmeal agar or on malt agar. No effect oflight on vegetative growth can be demonstrated. On the maltmedium, increased fruiting occurs with increase of nutrientup to 4 per cent, malt, but at higher concentrations fruitingis not increased and may be retarded. A chemically defined mediumwith starch as the carbon source allows fruiting, but at a lowlevel. Temperature has a profound effect on basidiocarp development;above 25 C. no fruit-bodies are normally formed although vegetativegrowth is approximately optimal at that temperature. For overallfruit-body production at 20 C, light above 100 lux is necessaryand light remains a limiting factor up to about 1, 000 lux.Under continuous light of suitable intensity, fruit-bodies continueto develop and discharge glebal-masses for many weeks. Thereis a distinct periodicity of discharge with (at 20 C.) about12 days between peaks of activity. This corresponds with thetime taken for basidiocarp initiation and development. A number of developmental stages of the basidiocarp are recognized.The final stage, glebal-mass discharge from stellately openedfruit-bodies, is indifferent to light, but all other stagesare stimulated by light. The light intensity for effective stimulationfalls during development and for the penultimate stage an intensityas low as 1 lux is effective. Only light of wave-length below500 mµ is active in overall basidiocarp development. Inthe sensitive region between 400 mµ and 500 mµ,there appear to be peaks of sensitivity around 440 mµand 480 mµ. In alternating light and darkness, simulating natural conditions,glebal-mass discharge occurs in the light periods. With a regimenof 24 hours light and 24 hours of darkness discharge is mainlyin the dark periods.     

Gravitational stress and lignification in aerial vs. submerged shoots of Hippuris vulgaris

Hippuris vulgaris L. is a heterophyllic aquatic plant that grows naturally under the different degrees of gravitational stress that are associated with submerged and aerial environments. This characteristic of H. vulgaris was exploited in order to study the interaction of gravitational stress with lignification processes. Lignin content was found to be 4.1% of aerial stem dry weight and 2.6% of submerged stem dry weight. The activity of phenylalanine ammonia-lyase (E.C. 4.3.1.5), an enzyme early in the lignin biosynthetic pathway, paralleled lignin content and was about 5 times higher in aerial than in submerged stems. Another lignin biosynthetic enzyme, peroxidase (E.C. 1.11.1.7), was studied, and although definite conclusions could not be drawn from measurements of total peroxidase activity, different isozyme patterns were observed in aerial and submerged-type shoots. Abscisic acid, which can induce the aerial-type shoot morphology on submerged shoots, probably is not involved in mediating changes in the lignin content of H. vulgaris . These results support the hypothesis that lignin biosynthesis is regulated by gravity.     

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.     

The effects of emersion on soluble carbohydrate accumulations in Hippuris vulgaris L.

The influence of emersion on carbohydrate accumulation in Hippuris vulgaris L. was studied by comparing the carbohydrate levels of fully submersed plants with those of plants producing emergent shoots.In all plant fractions, the dominant component was stachyose. It reached levels up to 34.6% dry matter.In both growth forms the green submersed parts contained between 2.12 (submersed plants) and 2.41 (plants with emergent apices) times more soluble carbohydrate, respectively, than the corresponding basal white parts. Another pool of carbohydrates was located in the emergent parts: the carbohydrate level of plants with emergent apical sections was about 8 times that of submersed plants.Emergent plants stored about 7 times more carbohydrate in the green submersed parts and 6.2 times more in the basal white parts than fully submersed plants.Thus the effects of direct access to atmospheric sources of CO₂, and the lack of any attenuation of irradiance by backscattering or absorbance in the water, achieved by aerial stems, are clearly evident in the different carbohydrate contents of submersed and emergent Hippuris plants.     

Light and pressure in two freshwater lakes and their influence on the growth, morphology and depth limits of Hippuris vulgaris

SUMMARY. Hippuris vulgaris was found growing down to a depth of 6 m in two clear-water lakes. Mean summer water temperatures of the epilimnia were 15–18°C. Midsummer photosynthetically available radiation, (PAR 400–700 nm) at 6 m was 100 μeinsteins m⁻²s⁻¹. In the laboratory, shoots of H. vulgaris continued to elongate at temperatures of 15 and 20°C and at pressures of 1.0, 1.8 and 2.3 atm. (corresponding to 0 m, 8.0 m and 13.3 m depths of water, respectively) providing PAR was kept above 100 °E m⁻²s⁻¹. Leaf primordia were initiated further from the apex in shoots grown under a pressure of 2.3 atm., but the site of initiation is not critical for the subsequent growth of leaves in H. vulgaris . Lacunae in shoots grown under a pressure of 2.3 atm. were also larger than those in control shoots, implying that pressure does not constrict air spaces. Root growth is not inhibited by a pressure of 2.3 atm. Field measurements and laboratory experiments indicate that in warm water, PAR is the environmental factor most likely to control the depth limits of H. vulgaris in the field.