Root Development and Source-Sink Relations in Carrot, Daucus carota L.

Growth analysis and ¹⁴CO₂ feeding experiments have shown thatthe developing storage organ became an increasingly importantsink for assimilates, accumulating 40% of the dry matter producedby the carrot plant within 9 weeks of sowing. The relative importanceof each leaf in fixing and exporting ¹⁴C was assessed at twostages of development. Morphogenetic responses indicated thatan absence of thickening in the lateral roots was associatedwith continued meristematic activity in the tap root, in theform of an elongating apex or a vascular cambium. Source-sink relations were examined by observing plant growthfollowing the removal of part of the tap root and/or lateralroots. Pruning the roots at 35 d reduced the subsequent growthof the plant by reducing the AGR of the remaining root systemand the shoot. The reduction in leaf growth was associated witha loss of fibrous roots, removal of part of the tap root havingvery little additional effect on shoot growth although the AGRof the root system was reduced by a further 78%. Increased fibrousroot RGRs following pruning soon re-established the normal fibrousroot/shoot ratio. These experiments demonstrated the importanceof the root system in controlling dry matter production in thecarrot plant, but suggested that the sink activity of the developingstorage organ was less significant than other root functions.     

Pervasive Mitochondrial Sequence Heteroplasmy in Natural Populations of Wild Carrot,Daucus carota spp. carota L

Exceptions to the generally accepted rules that plant mitochondrial genomes are strictly maternally inherited and that within-individual sequence diversity in those genomes, i.e., heteroplasmy, should be minimal are becoming increasingly apparent especially with regard to sequence-level heteroplasmy. These findings raise questions about the potential significance of such heteroplasmy for plant mitochondrial genome evolution. Still studies quantifying the amount and consequences of sequence heteroplasmy in natural populations are rare. In this study, we report pervasive sequence heteroplasmy in natural populations of wild carrot, a close relative of the cultivated crop. In order to assay directly for this heteroplasmy, we implemented a quantitative PCR assay that can detect and quantify intra-individual SNP variation in two mitochondrial genes (Cox1 and Atp9). We found heteroplasmy in > 60% of all wild carrot populations surveyed and in > 30% of the 140 component individuals that were genotyped. Heteroplasmy ranged from a very small proportion of the total genotype (e.g., 0.995:0.005) to near even mixtures (e.g., 0.590:0.410) in some individuals. These results have important implications for the role of intra-genomic recombination in the generation of plant mitochondrial genome genotypic novelty. The consequences of such recombination are evident in the results of this study through analysis of the degree of linkage disequilibrium (LD) between the SNP sites at the two genes studied.     

Endosperm and Embryo Development in Daucus carota L.

Maximum carrot seed dry weight and maximum endosperm volumewere reached about 35 d after anthesis, although at this timethe endosperm was still soft, the pericarp green and less than50% of the seeds were viable. Fully viable, ripe seeds werenot produced until 44 d later. Seventy per cent of the increasein endosperm volume was due to an increase in cell number, whichceased 35 d after anthesis. The increase in embryo volume wasslower and was due to an increase in both cell number and cellvolume which continued until 49 d after anthesis. At maturitythe embryo was the equivalent of between 2% and 3% of the endospermvolume. The relationship between embryo length and cell number per embryowas unaffected by seed crop plant density, seed crop harvestdate and position of the seed on the mother plant but it wasaffected by the year of seed production, possibly due to differencesin temperature during the period of seed growth. Key words: Endosperm, Embryo, Carrot, Development     

Dry Matter Distribution between the Shoot and Storage Root of Carrot (Daucus carota L.): I. Comparison of Varieties

The distribution of dry matter between shoot and storage rootof a wild variety and cultivars of carrot was investigated ina glasshouse experiment and a field experiment. In both experimentsthe deliberate introduction of variation in plant size revealeda linear relationship between the log weights of these partsat any time throughout growth. In the glasshouse experiment,in which growth was examined from approximately 10–600mg mean dry wt per plant, the slope of the relationship betweenIn shoot and In storage root dry wts decreased markedly duringdevelopment to 100 mg. Subsequently the slope became reasonablyconstant and the intercept progressively more negative. Datafrom the field experiment covered a similar timescale (48–115days) to the glasshouse experiment but the plants grew morequickly and were much heavier (180 mg–6 g dry wt). Therelationship between shoot and storage root for these data wassimilar to that for the plants of comparable size in the glasshouseexperiment. Over the range of development for which the slopeof the relationship was constant, data from both experimentswere described fairly well by the following equations: In shoot = – time+ In storage root where , and are constants. Between cultivars the slope ()and time constant () were similar, but the intercept () increasedwith maturity time of the cultivars. For wild carrot the slopewas larger and the time constant smaller than estimates forthe cultivars. These results on dry matter distribution arediscussed in relation to a model for partitioning assimilatein an individual plant. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, partitioning model     

Dry Matter Distribution Between the Shoot and Storage Root of Carrot (Daucus carota L.): II. Effect of Foliar Application of Gibberellic Acid

The effects of foliar sprays of gibberellic acid (GA) on drymatter distribution in carrots were investigated in three fieldexperiments between 1977 and 1979. The results were interpretedby using a simple quantitative model of assimilate partitioningbetween storage root and shoot. Although the response to GAvaried depending on the year in which the experiment was done,the model successfully described the effects of spraying time,GA concentration, planting density, plant age and cultivar.The maximum effects on repartitioning were achieved with concentrationsof 100–500 mg 1_–1 GA and, except for very earlyor late sprays, the effect was constant with time over a roughly4-week period. The multiplicative nature of the model was usefulin that despite the occurrence of various interactions, a similarassimilate partitioning response to GA in all four cultivarswas demonstrated. The model did not suggest an explanation forthe seasonal effects. Daucus carota L., carrot, assimilate distribution, dry matter distribution, storage root, gibberellic acid, partitioning model     

INHIBITION OF THE PHOTOSYNTHETIC CARBON DIOXIDE FIXATION OF GREEN PLANTS BY {alpha}-HYDROXYSULFONATES, AND ITS EFFECTS ON THE ASSIMILATION PRODUCTS

1. Several kinds of a-hydroxysulfonates, the bisulfite additioncompounds of aldehydes and ketones, were found to inhibit thephotosynthetic carbon dioxide fixation of the barley and wheatseedlings, tobacco leaf and Chlorella cells. Bisulfite additioncompounds of glyoxal, glyoxylate and benzaldehyde were moreeffective in this respect than those of formaldehyde and acetaldehyde.
2. The presence of -hydroxysulfonate causes an increase in ratiosof :¹⁴CO₂ incorporated in glycolate and alanine, and a decreasein incorporation in serine, malate, isocitrate and citrate.It was inferred that these changes are caused by the blockingof the formation of glyoxylate through inhibition of glycolicacid oxidase by the poison.
3. A reaction scheme was proposedto account for the above-statedresults, and the bearing ofthese findings on the possible roleof glycolic acid oxidasein the photosynthetic carbon dioxidefixation and in the formationof amino and organic acids wasdiscussed.

(Received December 8, 1961; )     

Vegetable Plant Part Relationships. III. Modification of Carrot (Daucus carota L.) Root and Shoot Weights by Gibberellic Acid and Daminozide

Aqueous foliar sprays of N-dimethylaminosuccinamic acid (daminozide)at 2000 p.p.m. and gibberellic acid (GA) at 100 p.p.m. wereapplied 45, 59, 82 and 100 days after sowing to Chantenay carrotswith population densities of 244, 495 and 883 plants m^–2.The plants were harvested on ten approximately weekly occasions;fresh weights were determined and d. wt estimates were obtainedfor the separated shoots (s) and roots (r). Allometric linearregressions of the logarithm of s on that of r at each harvestseparately, clearly showed that GA always increased shoot: rootratio and reduced root yield (by approximately 35 per cent)but could sometimes also increase whole-plant weight. Daminozideincreased root yield (by approximately 7 per cent from 80 tonnesha^–1) and tended to have effects opposite to those ofGA. Daucus carota L., carrot, root weight, shoot weight, N-dimethylaminosuccinamic acid (daminozide), gibberellic acid     

Effects of Mechanical Impedance on Root Growth in Barley (Hordeum vulgare L. ): I. EFFECTS ON THE ELONGATION AND BRANCHING OF SEMINAL ROOT AXES

Apparatus is described in which the root system of plants canbe exposed to accurately known external stresses in beds ofballotini for periods up to 3 weeks. A constant flow of aeratednutrient solution was supplied. Modifications of the apparatusallowed the emerging coleoptile also to be subjected to mechanicalstress. Earlier observations that roots are unable to decrease in diameterto enter small pores were confirmed. The effect of externalpressure on the rate of root elongation was independent of thediameter of pores provided this was smaller than the penetratingroot. Pressures of 20 and 50 kPa reduced the elongation of theseminal axes of barley by 50 and 80 per cent respectively. Significantreductions in root extension were also caused by 50 kPa or lessin more limited experiments with a number of other crop plants.The extension of the coleoptile and the first leaf respondedsimilarly to that of the roots. When the diameter of pores inthe rooting medium was intermediate between those of axes andlaterals, the former being impeded, an enhanced developmentof laterals led to a dense superficial root system. This considerablemodification of root form was without effect on nutrient uptakeprovided that an adequate supply of nutrients was availablein the restricted rooting zone. Attention is directed to some of the implications of these responsesfor plant growth under field conditions. However, considerationof the physiological mechanisms responsible for the effectsof low external pressures and the changes in cell structureto which they lead are deferred to subsequent papers.     

Vegetable Plant Part Relationships. I. Effects of Time and Population Density on the Shoot and Storage Root Weights of Carrot (Daucus carota L.)

Chantenay carrot plants were grown in replicated plots containingdensities of 25, 64, 130 and 245 plants m^–2 and harvestedon 20 weekly occasions giving a total of 360 pairs of d. wtsand 13908 pairs of f. wts of shoots (s) and roots (r). The relationshipbetween the logarithms of s and r was curved for plants sampledon successive occasions from the same density but it was linearfor plants sampled on a single occasion, both within and betweendensities. A good overall relationship was In s = a+0.805 In r, where the intercept (a) ranged in approximately equal stepsfrom +1.2 to –1.1 at the first and last harvests respectively.Except for some systematic deviation from this equation at earlyharvests, the above relationship fitted the data well irrespectiveof the wide range of density and whole plant weight. Daucus carota L. carrot, root/shoot weight, population density, growth analysis     

EFFECTS OF PHOTOCYCLES AND PERIODIC AMMONIUM SUPPLY ON THREE MARINE PHYTOPLANKTON SPECIES. II. AMMONIUM UPTAKE AND ASSIMILATION1

The relative influence of the photoperiod and of periodic ammonium pulses in entraining the cell division cycle in nitrogen-limited cyclostat cultures differs dramatically in Hymenomonas carterae Braarud and Fagerl, Amphidinium carteri Hulburt and Thalassiosira weissflogii Grun. We examined how each species processes an NH₄⁺ pulse at various times during the cell cycle and the L/D cycle. Rates of NH₄⁺ uptake and changes in cellular concentrations of NH₄⁺, free amino acids, and protein were examined after the addition of an NH₄⁺ pulse. Depletion of NH₄⁺ from the medium occurred earlier when the pulse was given at the beginning of the light period than at the beginning of the dark period in H. carterae and A. carteri. Depletion took longer in the T. weissflogii cultures and the kinetics were similar during both stages of the photocycle in this species. Similarly, the temporal phasing and maximum pool sizes varied with timing of the NH₄⁺ pulse in H. carterae and A. carteri but complete assimilation was relatively rapid. More persistent pools of NH₄⁺ and free amino acids accumulated in T. weissflogii, and the patterns of assimilation varied little as a function of the timing of the pulse with respect to the photocycle. Although nitrogen metabolism occurred rapidly in nitrogen-limited H. carterae and A. carteri, the entrainment of the cell division cycle by the photoperiod resulted in a large degree of uncoupling between completion of nitrogen assimilation and cell division. It is hypothesized that the strong entrainment of the cell division cycle of T. weissflogii by NH₄⁺ pulses results from a relatively slow rate of nitrogen metabolism.