Regrowth of western wheatgrass utilizing 14C-labeled assimilates stored in belowground parts

Summary Results of this study showed that carbohydrates stored in the roots of western wheatgrass are utilized for regrowth following clipping of the aboveground foliage. Shoots remained dependent on carbohydrates stored in roots until sufficient photosynthetic leaf surface was developed to supply carbon to the shoots. During early phenophases, the partitioning of carbohydrates between shoots and roots was identical, indicating equal metabolic demands for carbon from both the shoot and root systems. Subsequent fluctuations in root and shoot carbohydrates may be caused by selected pressure imposed on either the root or shoot systems by physiological changes in these organs.Respiratory losses of ¹⁴C were slower during the early phenophases which may indicate that either the rate of respiration was slower or that recently assimilated nonlabeled carbon sources were utilized for respiration instead of the endogenous sources assimilated earlier in the growth period. re]19760427     

Effect of crude seaweed extracts on seed germination, seedling growth and some metabolic processes of Vicia faba L

Crude extracts from three green seaweeds (Cladophora dalmatica, Enteromorpha intestinalis, Ulva lactuca) and the three red algae (Corallina mediterranea, Jania rubens, Pterocladia pinnate) were prepared. Their effects on germination, growth of seedlings, chlorophyll content and other metabolic activities of Vicia faba were investigated. The crude extract of C. dalmatica showed maximal activity, and it increased seed germination, length of main root and shoot systems and the number of lateral roots. All the crude extracts of seaweed increased protein content in both root and shoot systems, total soluble sugars and chlorophyll content in leaves. The cytokinin content of the green algae was higher than that in red algae. Growth of seedlings of V. faba was stimulated but to different degrees.     

Effects of flooding the root system of sunflower plants on the cytokin in content in the xylem sap

The severe chlorosis observed in the lower most of flooded sunflower plants (Helianthus annuus L. cv. Tall Single) may lie initiated by a reduction in the import of cytokinins by the stoot from the flooded root system. Experiment indicates that during 12 hours following the release of flooding, plants previously flooded for 72 hours or less recover their ability to exude sap when the root systems are aerated, and the root systems synthesize and export amino-acids to the shoot. Plants flooded for longer periods lose these abilities. The metabolic activity of the root apices declines parallel with the decline in eytnkinin concentration in the sap with increase in flooding time up to 72 hours. Flooding for 96 hours drastically reduce all four parameters of root activity. After flooding for this period there was a large increase in the number of blackened and tetrazolium-negative root apices which were in all probability dead. The correlation between the metabolic activity of the root apices and the total cytokinin content of the sap supports tbe view that root apices may be sites of cytokinin synthesis.     

Nodulation phenotypes of gibberellin and brassinosteroid mutants of pea

The initiation and development of legume nodules induced by compatible Rhizobium species requires a complex signal exchange involving both plant and bacterial compounds. Phytohormones have been implicated in this process, although in many cases direct evidence is lacking. Here, we characterize the root and nodulation phenotypes of various mutant lines of pea (Pisum sativum) that display alterations in their phytohormone levels and/or perception. Mutants possessing root systems deficient in gibberellins (GAs) or brassinosteroids (BRs) exhibited a reduction in nodule organogenesis. The question of whether these reductions represent direct or indirect effects of the hormone deficiency is addressed. For example, the application of GA to the roots of a GA-deficient mutant completely restored its number of nodules to that of the wild type. Grafting studies revealed that a wild-type shoot or root also restored the nodule number of a GA-deficient mutant. These findings suggest that GAs are required for nodulation. In contrast, the shoot controlled the number of nodules that formed in graft combinations of a BR-deficient mutant and its wild type. The root levels of auxin and GA were similar among these latter graft combinations. These results suggest that BRs influence a shoot mechanism that controls nodulation and that the root levels of auxin and GA are not part of this process. Interestingly, a strong correlation between nodule and lateral root numbers was observed in all lines assessed, consistent with a possible overlap in the early developmental pathways of the two organs.     

Two ways to skin a plant: The analysis of root and shoot epidermal development in Arabidopsis

The post-embryonic architecture of higher plants is derived from the activity of two meristems that are formed in the embryo: the shoot meristem and the root meristem. The epidermis of the shoot is derived from the outermost layer of cells covering the shoot meristem through repeated anticlinal divisions. By contrast, the epidermis of the root is derived from an internal ring of cells, located at the centre of the root meristem, by a precise series of both periclinal and anticlinal divisions. Each epidermis has an independent origin. In Arabidopsis the mature shoot epidermis is composed of a small number of cell types: hair cells (trichomes), stomatal guard cells and other epidermal cells. In shoots, hairs take the form of branched trichomes that are surrounded at their base by a ring of accessory cells in a sheet of epidermal cells. The root epidermis is composed of two cell types: trichoblasts that form root hair cells and atrichoblasts that form non-hair cells. Mutations affecting both the patterning and the morphogenesis of cells in both shoot and root epidermis have recently been described. Most of these mutations affect development in a single epidermis, but at least one, ttg, is involved in development in both epidermal systems.     

The Effect of Photon Flux Density and Duration of the Photosynthetic Period on Growth and Dry Matter Distribution in Carrot

The distribution of dry matter between shoot and storage rootof carrot plants grown in light regimes varying in intensity,duration and integral, is used to test an hypothesis for thecontrol of assimilate partition Results from seven varietiesshow that shoot to storage root weight ratios are affected bythe light environment, but that these effects are associatedwith the effect of light on plant size It is concluded thatquantitative alterations to the supply of assimilate, resultingfrom variation in the light regime, do not affect its partitionto different organs This is discussed in relation to other investigationswhich have suggested a relationship between the duration ofthe photosynthetic period, assimilate sequestration in foliarstarch and partition between shoot and root Daucus carota L, carrot, assimilate partition, light intensity, daylength, shoot, storage root, shoot-root ratio, source-sink relations     

Interactions between root and shoot competition vary among species

Understanding how the competition varies with productivity is essential for differentiating among alternative models of plant community organization. Prior attempts to explain shifts in root and shoot competition along gradients have generally assumed an additive interaction between the two competitive forms, using an experimental design which does not fully separate both above‐ and belowground processes. At the most basic level, few field studies have separated root and shoot competition, and we have limited knowledge about both the relative importance of these processes, and how they interact to affect plant growth in the field. Presented here are findings from a field study in which root and shoot competition were experimentally separated by using root exclusion tubes and neighbor tiebacks in an early successional community. Individuals of four species (Abutilon theophrasti, Amaranthus retroflexus, Rumex crispus, and Plantago lanceolata) were grown at two levels of fertilization with full competition, aboveground competition only, belowground competition only, or neither above‐ nor belowground competition. Competition was measured as competitive response, which is the natural log of the relative biomass of a target plant grown with competition compared to growth without competition. In contrast to predictions from current models of productivity‐competition relationships, but in agreement with other experimental studies, there was no change in the strengths or root, shoot, or total competition with a modest increase in productivity. Despite no effect of fertilization on the strength of competition, the form of interaction between root and shoot competition varied both as a function of species identity and fertilization. For both of the rosette forming species, the combined effects of root and shoot competition were less than predicted assuming no interaction (a “negative interaction”), with one species switching from a negative to an additive interaction with fertilization. The fact that fertilization caused a shift in the root‐shoot interaction, but not in the total strength of root and shoot competition, suggests that the root‐shoot interaction is itself a highly labile variable. If root‐shoot interactions are common in natural systems, then simply measuring the strength of one form of competition in no way provides any information about the overall importance of that competitive form to plant growth.     

Root Respiration in White Spruce (Picea glauca [Moench] Voss) Seedlings in Relation to Morphology and Environment

Roots of white spruce seedlings (Picea glauca [Moench] Voss) undergo respiratory changes during the year that are related to changing metabolic requirements. An alternative pathway is always present, functions during most of the year, and operates maximally during periods of root and shoot growth. Although some differences in respiration and the apportioning of respiration can be correlated to root morphology, the environment and the stage of shoot development are also important controls. Differences in respiration related to root morphology are not manifest in mitochondrial structure, but overall rates were found to correlate with the number of mitochondria present. Root respiration in seedlings grown under root growth capacity conditions reflects root and shoot growth at that time rather than root growth capacity.     

The Rate of Growth and Partitioning of Assimilates in Young Grass Plants: A Mathematical Model

A model describing the increase in weight with time of younggrass plants is formulated. The parameters are the relativegrowth rates of the root and shoot systems; k, the ratio ofthe relative growth rate of the root system relative to thatof the shoot system; b, the weight of the root system when thatof the shoot system is unity, and u the rate of increase inweight of the whole plant per unit of shoot system per unitof time, k and b are the constants in the allometric formula,r = bs^k where r and are the weights of the root and shoot systems.The model enables the effect of changes in the distributionof assimilates between the root and shoot systems upon the rateof growth of the plant to be assessed. Data from a number ofexperiments are analysed in this manner and the significanceof the results discussed.     

Ara-Rhizotron: An Effective Culture System to Study Simultaneously Root and Shoot Development of Arabidopsis

Studying Arabidopsis thaliana (L.) Heynh. root development in situ at the whole plant level without affecting shoot development has always been a challenge. Such studies are usually carried out on individual plants, neglecting competition of a plant population, using hydroponic systems or Agar-filled Petri dishes. Those both systems, however, present some limitations, such as difficulty to study precisely root morphogenesis or time-limited culture period, respectively. In this paper, we present a method of Arabidopsis thaliana (L.) Heynh. cultivation in soil medium, named “Ara-rhizotron”. It allows the non-destructive study of shoot and root development simultaneously during the entire period of vegetative growth. In this system, roots are grown in 2D conditions, comparable to other soil cultures. Moreover, grouping several Ara-rhizotrons in a box enables the establishment of 3D shoot competition as for plants grown in a population. In comparison to a control culture grown in pots in the same environmental conditions, the Ara-rhizotron resulted in comparable shoot development in terms of dry mass, leaf area, number of leaves and nitrogen content. We used this new culture system to study the effect of irrigation modalities on plant development. We found that irrigation frequency only affected root partitioning in the soil and shoot nitrogen content, but not shoot or root growth. These effects appeared at the end of the vegetative growth period. This experiment highlights the opportunity offered by the Ara-rhizotron to point out tardy effects, affecting simultaneously shoot development and root architecture of plants grown in a population. We discuss its advantages in relation to root development and physiology, as well as its possible applications.     

How do plants respond to nutrient shortage by biomass allocation?

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.     

Dissecting the effects of nitrate, sucrose and osmotic potential on Arabidopsis root and shoot system growth in laboratory assays

Studying the specific effects of water and nutrients on plant development is difficult because changes in a single component can often trigger multiple response pathways. Such confounding issues are prevalent in commonly used laboratory assays. For example, increasing the nitrate concentration in growth media alters both nitrate availability and osmotic potential. In addition, it was recently shown that a change in the osmotic potential of media alters the plant's ability to take up other nutrients such as sucrose. It can also be difficult to identify the initial target tissue of a particular environmental cue because there are correlated changes in development of many organs. These growth changes may be coordinately regulated, or changes in development of one organ may trigger changes in development of another organ as a secondary effect. All these complexities make analyses of plant responses to environmental factors difficult to interpret. Here, we review the literature on the effects of nitrate, sucrose and water availability on root system growth and discuss the mechanisms underlying these effects. We then present experiments that examine the impact of nitrate, sucrose and water on root and shoot system growth in culture using an approach that holds all variables constant except the one under analysis. We found that while all three factors also alter root system size, changes in sucrose and osmotic potential also altered shoot system size. In contrast, we found that, when osmotic effects are controlled, nitrate specifically inhibits root system growth while having no effect on shoot system growth. This effectively decreases the root : shoot ratio. Alterations in root : shoot ratio have been widely observed in response to nitrogen starvation, where root growth is selectively increased, but the present results suggest that alterations in this ratio can be triggered across a wide spectrum of nitrate concentrations.     

Fine-tuning by strigolactones of root response to low phosphate

Strigolactones are plant hormones that regulate the development of different plant parts. In the shoot,they regulate axillary bud outgrowth and in the root,root architecture and root-hair length and density. Strigolactones are also involved with communication in the rhizosphere,including enhancement of hyphal branching of arbuscular mycorrhizal fungi. Here we present the role and activity of strigolactones under conditions of phosphate deprivation.Under these conditions,their levels of biosynthesis and exudation increase,leading to changes in shoot and root development. At least for the latter,these changes are likely to be associated with alterations in auxin transport and sensitivity. On the other hand,strigolactones may positively affect plant–mycorrhiza interactions and thereby promote phosphate acquisition by the plant. Strigolactones may be a way for plants to fine-tune their growth pattern under phosphate deprivation.     

Adverse Effect of Shoot Growth on Root Growth in Rooted Cuttings of Aspen

In experiments with rooted cuttings of aspen (Populus tremula L). with a small leaf area, it was found that the roots grew well as long as there was no shoot growth. The onset of shoot growth was followed by a period of decreased root growth. When the leaf area had increased sufficiently, root growth recovered. Decreasing the shoot growth by removal of growth points in the shoot or by short day treatment increased the fraction of photosynthesis products used for root growth, leading to increased root/shoot ratios. Competition between growing shoots and roots for carbohydrates formed in photosynthesis is considered to cause the effects noted and to be of importance for maintaining the balance between the root and shoot systems.     

Chemical Derivatization of Metabolite Mass Profiling of the Recretohalophyte <Emphasis Type="Italic">Aeluropus lagopoides</Emphasis> Revealing Salt Stress Tolerance Mechanism

Plants are the primary producers of food for human being. Their intracellular environment alternation is influenced by abiotic stress factors such as drought, heat and soil salinity. Aeluropus lagopoides is a strong halophyte that grows with ease under high saline muddy banks of creeks of Gujarat, India. To study the response of salinity on metabolite changes in Aeluropus, three treatments, i.e. control, salinity and recovery, were selected for both shoot and root tissue. The cytosolic metabolite state was analysed by molecular chemical derivatization gas chromatography mass profiling. During saline treatment, significant increase of compatible solutes in shoot and root tissue was observed as compared to control. Subsequently, metabolic concentration decreased under recovery conditions. The metabolites like amino acids, organic acids and polyols were significantly detected in both shoot and root of Aeluropus under salinity. The metabolites like proline, aspartic acid, glycine, succinic acid and glycolic acid were significantly upregulated under stress. The salicylic acid was found to play a role in maintaining the polyols level by its down-regulation during salinity. The principle component analysis of all detected metabolites in both shoot and root showed that metabolites expressed under salinity (component 1) were highly variable, while metabolites expressed under recovery (component 2) were comparatively less variable as compared to control. The evolved intracellular compartmentalization of amino acids, organic acids and polyols in A. lagopoides can be a hallmark to sustaining at high salinity stress.     

The effect of aeration of the nutrient solution on the growth ofLolium perenne

Summary Additional aeration increased the growth of both the root and shoot systems, the relative increase depending upon the genetic constitution of the plant. The increase in growth of a particular clone brought about by additional aeration was proportional to its growth without additional aeration. Aeration also increased the plants' Net Assimilation Rate and reduced the proportion of air-space in the tissues of the leaves and particularly of the roots. The growth of the plant was related to the amount of air-space in the roots, whether the plant was receiving additional aeration or not. It is suggested that aeration affects several metabolic processes and that the relative effects vary with the genetic constitution of the plant.