Asynchronicity in root and shoot phenology in grasses and woody plants

Phenology is central to understanding vegetation response to climate change, as well as vegetation effects on plant resources, but most temporal production data is based on shoots, especially those of trees. In contrast, most production in temperate and colder regions is belowground, and is frequently dominated by grasses. We report root and shoot phenology in 7‐year old monocultures of 10 dominant species (five woody species, five grasses) in southern Canada. Woody shoot production was greatest about 8 weeks before the peak of root production, whereas grass shoot maxima preceded root maxima by 2–4 weeks. Over the growing season, woody root, and grass root and shoot production increased significantly with soil temperature. In contrast, the timing of woody shoot production was not related to soil temperature (r=0.01). The duration of root production was significantly greater than that of shoot production (grasses: 22%, woody species: 54%). Woody species produced cooler and moister soils than grasses, but growth forms did not affect seasonal patterns of soil conditions. Although woody shoots are the current benchmark for phenology studies, the other three components examined here (woody plant roots, grass shoots and roots) differed greatly in peak production time, as well as production duration. These results highlight that shoot and root phenology is not coincident, and further, that major plant growth forms differ in their timing of above‐ and belowground production. Thus, considering total plant phenology instead of only tree shoot phenology should provide a better understanding of ecosystem response to climate change.     

Transpiration efficiency and apparent cuticular transpiration in some c3 and c4 plants

Amphistomatous C₃ (Nicotiana tabacum L., Datura stramonium L.) and C₄ (Sorghum saccharatum Pers. and Zea mays L.) species were examined to find how (if at all) their inherent differences in water-use economy are reflected in apparent cuticular transpiration or vice versa. Transpiration efficiency (TE) was calculated from steady state photosynthesis (A) and transpiration (E) rates estimated for the upper side of the leaf after light induction of stomata opening. Apparent cuticular transpiration (’E_c) was measured as the part of transpiration which was not eliminated by convective counteraction of the air stream passing across the amphistomatous leaf: total pressure difference (AP) across the leaf was increased and the minimal value of E_ΔPτ0 was taken as the apparent cuticular transpiration rate (’E_c). ’E_c was treated relative to E at AP equal to zero (E_GDP=0), E’_cr. Measurements were carried out under two leaf-air vapour pressure differences (VPD). E_r (i.e. E_GDPτ0/E_GDP=0) versus GDP patterns differed qualitatively between the investigated C₃ and C₄ plants. TE increased and ’E_cr decreased from tobacco, stramony, maize to sorghum for both VPD of air. ’E_cr and TE were approximately linearly related, the slope being dependent on VPD. The increase in VPD resulted in larger E and slightly smaller epidermal conductance (g) at GDP equal to zero. Both E’_cr and E’_cr decreased markedly at the same time especially, for species with high TE. The results were considered as an indirect confirmation that E’_c values estimated by the technique used reflect species-specific differences in external peristomatal and cuticular vapour loss, at least in a relative sense.     

Nitrogenase activity in the rhizosphere of sugar cane and some other tropical grasses

Summary Roots of sugar cane had considerable nitrogenase activity and produced up to 5 n moles ethylene/h/g root by the reduction of acetylene. The rhizosphere soil and soil mid-way between the cane rows also reduced acetylene.Beijerinckia indica was abundant on roots and in the soil. Nitrogenase activity was also associated with roots ofPanicum maximum,Pennisetum purpureum andCymbopogon citratus.     

Development of root systems during the growth of some vegetable crops

Summary The development of the root system of some locally important vegetable crops has been studied. The crops investigated were grown under mediterranean and tropical conditions with appropriate cultural treatment.The development of root systems was more a reflection of soil conditions than a conformation to a growth pattern specific for the particular crop plant. Evidence for the restricting effect of greater soil bulk density on root development and a relation between soil bulk density and depth of root development was obtained. Frequent irrigation is considered to be a factor Inducing shallow root development and also a lack of nutrients in the deep layers of soil.Distinct asymetric development of the root system was correlated with the pattern of distribution of the irrigation water.     

Co-ordinated growth between aerial and root systems in young apple plants issued from in vitro culture

BACKGROUND AND AIMS: In several species exhibiting a rhythmic aerial growth, the existence of an alternation between root and shoot growth has been demonstrated. The present study aims to investigate the respective involvement of the emergence of new organs and their elongation in relation to this phenomenon and its possible genotypic variation in young apple plants. METHODS: Two apple varieties, X6407 (recently named 'Ariane') and X3305 ('Chantecler' x 'Baujade'), were compared. Five plants per variety, issued from in vitro culture, were observed in minirhizotrons over 4 months. For each plant, root emergence and growth were observed twice per week. Growth rates were calculated for all roots with more than two segments and the branching density was calculated on primary roots. On the aerial part, the number of leaves, leaf area and total shoot length were observed weekly. KEY RESULTS: No significant difference was observed between varieties in any of the final characteristics of aerial growth. Increase in leaf area and shoot length exhibited a 3-week rhythm in X3305 while a weaker signal was observed in Ariane. The primary root growth rate was homogeneous between the plants and likewise between the varieties, while their branching density differed significantly. Secondary roots emerged rhythmically, with a 3-week and a 2-week rhythm, respectively, in X3305 and 'Ariane'. Despite a high intra-variety variability, significant differences were observed between varieties in the secondary root life span and mean length. A synchronism between leaf emergence and primary root growth was highlighted in both varieties, while an opposition phase was observed between leaf area increments and secondary root emergence in X3305 only. CONCLUSION: A biological model of dynamics that summarizes the interactions between processes and includes the assumption of a feedback effect of lateral root emergence on leaf emergence is proposed.     

Levels of oxygenated Fatty acids in young corn and sunflower plants

Three oxygenated unsaturated fatty acids were investigated to determine whether they were present in seedlings of corn (Zea mays L. cv. NK PX443) and sunflower (Helianthus annuus L. cv. Sundak). The three compounds, 13-hydroxy-12-oxo-cis-9-octadecenoic acid (I), 13-hydroxy-12-oxo-cis,cis-9, 15-octadecadienoic acid (II), and 12-oxo-cis,cis-10, 15-phy-todienoic acid (III), were detected and estimated by gas chromatography-mass spectrometry selected ion monitoring of their trimethylsilyloxy, methyloxime derivatives with 20-carbon analogs added as internal standards. In corn, the concentration of III increased between 5 and 10 days, while I and II remained relatively constant. A higher concentration of II was observed in corn seedlings grown in the light than those grown in the dark. Wounding increased the levels of all three compounds. In sunflower seedlings, the concentrations of I, II, and III increased between 6 and 10 days. The intracellular concentration of III in 10-day-old light-grown seedlings was estimated to be 200 nm in corn and 40 nm in sunflower.     

Seasonal water uptake and movement in root systems of Australian phraeatophytic plants of dimorphic root morphology: a stable isotope investigation

A natural abundance hydrogen stable isotope technique was used to study seasonal changes in source water utilization and water movement in the xylem of dimorphic root systems and stem bases of several woody shrubs or trees in mediterranean-type ecosystems of south Western Australia. Samples collected from the native treeBanksia prionotes over 18 months indicated that shallow lateral roots and deeply penetrating tap (sinker) roots obtained water of different origins over the course of a winter-wet/summer-dry annual cycle. During the wet season lateral roots acquired water mostly by uptake of recent precipitation (rain water) contained within the upper soil layers, and tap roots derived water from the underlying water table. The shoot obtained a mixture of these two water sources. As the dry season approached dependence on recent rain water decreased while that on ground water increased. In high summer, shallow lateral roots remained well-hydrated and shoots well supplied with ground water taken up by the tap root. This enabled plants to continue transpiration and carbon assimilation and thus complete their seasonal extension growth during the long (4–6 month) dry season. Parallel studies of other native species and two plantation-grown species ofEucalyptus all demonstrated behavior similar to that ofB. prionotes. ForB. prionotes, there was a strong negative correlation between the percentage of water in the stem base of a plant which was derived from the tap root (ground water) and the amount of precipitation which fell at the site. These data suggested that during the dry season plants derive the majority of the water they use from deeper sources while in the wet season most of the water they use is derived from shallower sources supplied by lateral roots in the upper soil layers. The data collected in this study supported the notion that the dimorphic rooting habit can be advantageous for large woody species of floristically-rich, open, woodlands and heathlands where the acquisition of seasonally limited water is at a premium.     

The relation of root systems to shoot systems in vascular plants

The roots and shoots of vascular plants may be positionally and developmentally related in various ways. However, botanical teaching and research are strongly influenced by the paradigmatic annual dicotyledon, whose bipolar embryo develops into a plant with root and shoot meeting only at the hypocotyl. In 1930 Goebel criticized this example as a general model for plants, proposing instead the opposed concepts “allorhizy” (referring to plants whose root and shoot are related as above) and “homorhizy”(referring to plants without a bipolar embryo, all of whose roots are shoot-borne, e.g., pteridophytes). Goebel’s approach permeates the extensive German morphological literature, but has been virtually ignored in English-language literature. The allorhizy/homorhizy dichotomy has proved heuristic. However, it suggests a correlation between embryo type and mature morphology that does not always hold. Furthermore, it does not take into account the root-borne shoots typical of many plant species. Finally, Goebel’s presentation of the terms (which he does not explicitly define) creates ambiguity as to whether they designate structural concepts or the attributes of evolutionary groups. The alternative proposed here is a structural analysis of the possible topological relationships among root and shoot systems. Each structural class is then considered with regard to embryo types, potential for clonal growth and other ecological correlates, and phylogenetic distribution. This approach provides both a test of Goebel’s concepts and a basis for further comparative study of wholeplant form.     

Development of the root crown in some conifers

Summary Large and small stumps of 3 spruce species, a pine, a fir and hemlock were pulled up from 15 year plantations. Roots originating from the root crown were counted (<0.5 cm) or, if larger, their diameters were measured, taper, eccentricity, compass bearing, inclination, position on the rootstock and basal age (by annual rings). The sequence of events leading to the developed skeletal root system was reconstructed. Hypotheses to account for the distinct populations of roots were examined. In all species, major roots originated between 2 and 7 yrs after planting and grew thicker and more eccentric at their bases than minor roots of the same age. Positively geotropic roots were distinct from plagiogeotropic roots.     

Localization of glycerate kinase and some enzymes for sucrose synthesis in c(3) and c(4) plants

The localization of some key enzymes leading to sucrose synthesis in photosynthetic tissue of C₃ and C₄ species was investigated. These included UDP-glucose (UDPG) pyrophosphorylase, sucrose phosphate synthetase, and glycerate kinase. Whether glycerate kinase is localized exclusively in the chloroplast or partly outside the chloroplast could influence the fate of carbon flow to sucrose through the glycolate pathway.     

Variation in the activity of some enzymes of photorespiratory metabolism in C4 grasses

BACKGROUND AND AIMS: Photorespiration occurs in C4 plants, although rates are small compared with C3 plants. The amount of glycine decarboxylase in the bundle sheath (BS) varies among C4 grasses and is positively correlated with the granal index (ratio of the length of appressed thylakoid membranes to the total length of all thylakoid membranes) of the BS chloroplasts: C4 grasses with high granal index contained more glycine decarboxylase per unit leaf area than those with low granal index, probably reflecting the differences in O2 production from photosystem II and the potential photorespiratory capacity. Thus, it is hypothesized that the activities of peroxisomal enzymes involved in photorespiration are also correlated with the granal development. METHODS: The granal development in BS chloroplasts was investigated and activities of the photorespiratory enzymes assayed in 28 C4 grasses and seven C3 grasses. KEY RESULTS: The NADP-malic enzyme grasses were divided into two groups: one with low granal index and the other with relatively high granal index in the BS chloroplasts. Both the NAD-malic enzyme and phosphoenolpyruvate carboxykinase grasses had high granal index in the BS chloroplasts. No statistically significant differences were found in activity of hydroxypyruvate reductase between the C3 and C4 grasses, or between the C4 subtypes. The activity of glycolate oxidase and catalase were smaller in the C4 grasses than in the C3 grasses. Among the C4 subtypes, glycolate oxidase activities were significantly smaller in the NADP-malic enzyme grasses with low granal index in the BS chloroplasts, compared with in the C4 grasses with substantial grana in the BS chloroplasts. CONCLUSIONS: There is interspecies variation in glycolate oxidase activity associated with the granal development in the BS chloroplasts and the O2 production from photosystem II, which suggests different potential photorespiration capacities among C4 grasses.     

Composition and nutritive value of some grasses, plants and aquatic weeds tested as diets

The composition and nutritive value of different diets, namely the aquatic weeds— Hydrilla verticillata (L.f.) Presl., Lemna gibbs (L.) Pistia stratiotes (L.), grasses—Guinea grass Panicum maximum Jacq., Napier grass Pennisetum purpureum Schum. and plants—sweet potato leaves Ipomaea batatas L. and tapioca leaves Manihot utilissimus Pohl. were determined and compared. The diets contained 13.5 to 30.48% protein; 1.89 to 9.60% fat; 3.94 to 23.13% ash; 5.42 to 26.70% fibre and 24.87 to 46.27% carbohydrate. Most of the minerals determined in the aquatic weeds were higher than those in grasses and plants. The feeding of Hydrilla , Napier grass and tapioca leaves to grass carp Ctenopharyngodon ideltus (V.) showed a different growth rate and the results obtained indicated the superiority of Hydrilla diet over Napier grass and tapioca leaves.     

Variation in amounts of pyruvate, orthophosphate dikinase, and some other enzymes of the c(4) pathway in some wheat species

First leaves and flag leaves of the wheat species Triticum aestivum cv Anza (6×), T. boeoticum Boiss (2×) L. were examined for content of pyruvate, orthophosphate dikinase (PPDK), phosphoenolpyruvate carboxylase (PEPC), and ribulose 1,5-bisphosphate carboxylase (RuBPC) by protein blot analyses using antibodies to maize leaf enzymes and by activity assays. In agreement with previous reports, the amount of RuBPC per mesophyll cell was about 3 times more in the hexaploid species, T. aestivum, than in the diploid species, T. boeoticum, both in first leaves and in flag leaves. In contrast, the level of PPDK polypeptide was nearly 3-fold higher per unit leaf area in the first leaf and 63% higher in the flag leaf of this diploid species compared to this hexaploid species. There was no significant difference in the levels of polypeptide and enzyme activity of PEPC between diploid and hexaploid wheat. Despite this significantly greater level of PPDK in the diploid species, the actual amount of PPDK could still supply only a limited amount of the enzyme activity necessary to provide phosphoenolpyruvate (PEP) for any putative intracellular C₄ carbon shuttle providing carbon to RuBPC. Thus, this difference in enzyme amount could not by itself account for the reported high rates of net photosynthesis at high light intensity in T. boeoticum. Together with reported anatomical differences between the diploid and hexaploid species, however, this biochemical difference may be of physiological importance.     

Influence of root temperature on the potassium requirements of young tomato plants

The effect of low root temperature on the growth and K requirements of young tomato (Lycopersicon esculentum Mill. cv Sonatine) plants was investigated. When K was supplied in solution at high concentration (5 mM), lowering the temperature of the root system from 25° to 15°C reduced the relative growth rate so that after ten days plant dry weight was 60% and leaf area 44% of that of controls maintained at 25°C. Shoot: root dry weight ratio was initially increased by cooling, but declined to 84% of controls after ten days. In spite of these changes in shoot: root ratio the concentration of K in whole plants, expressed on the basis of tissue water, was stable throughout the experiment and was significantly higher than that of controls. Further, the critical concentration of K for shoots (the concentration in the shoot associated with 90% maximum growth) was also increased at root temperatures of 15° and 30°C compared with 24°C. It is suggested that the higher concentration of K at low root temperature may reflect a real increase in requirement for the element at the physiological level. Preliminary measurements of the solute potential demonstrated a less osmotically active sap in leaves of root-cooled plants, thus there may be a greater reliance on K as an osmoticum in these individuals. When supplies of K limited growth, root-cooling had no effect on any of the parameters determining the efficiency of its use; the minimum concentration to which roots could deplete the solution of K was identical for cooled and control plants and at the same stage of visible deficiency there was no significant difference in the efficiency ratio (mg DW, mg^-1 K) or utilization efficiency (mg DW mM ^-1 K), in spite of large differences in the partitioning of dry matter.     

Information capacity of single cells in some sensory systems

For three sensory systems where the frequency response is known, and the spectral properties of the modulated output discharge have been studied, the information capacity is calculated by one model of continous channels. The hypotheses and the limits underlying the use of the model are stated, the results are discussed.     

The relationship between sublethal water saturation deficit and the dynamics of soil moisture in some xerophilous grasses

The paper deals with the resaturation of water saturation deficit in fourStipa species tested under various ecological conditions. Attention is paid to the relations between the saturation and oversaturation types of curves, on the one hand, and soil moisture on the other. The oversaturation type appears in plants well supplied with soil moisture. The explanation of this phenomenon is discussed.     

Detoxification of corn antimicrobial compounds as the basis for isolating Fusarium verticillioides and some other Fusarium species from corn.

The preformed antimicrobial compounds produced by maize, 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and its desmethoxy derivative 2,4-dihydroxy-2H-1,4-benzoxazin-3-one, are highly reactive benzoxazinoids that quickly degrade to the antimicrobials 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA), respectively. Fusarium verticillioides (= F. moniliforme) is highly tolerant to MBOA and BOA and can actively transform these compounds to nontoxic metabolites. Eleven of 29 Fusarium species had some level of tolerance to MBOA and BOA; the most tolerant, in decreasing order, were F. verticillioides, F. subglutinans, F. cerealis (= F. crookwellense), and F. graminearum. The difference in tolerance among species was due to their ability to detoxify the antimicrobials. The limited number of species having tolerance suggested the potential utility of these compounds as biologically active agents for inclusion within a semiselective isolation medium. By replacing the pentachloronitrobenzene in Nash-Snyder medium with 1.0 mg of BOA per ml, we developed a medium that resulted in superior frequencies of isolation of F. verticillioides from corn while effectively suppressing competing fungi. Since the BOA medium provided consistent, quantitative results with reduced in vitro and taxonomic efforts, it should prove useful for surveys of F. verticillioides infection in field samples.