The making of giant pumpkins: how selective breeding changed the phloem of Cucurbita maxima from source to sink

Despite the success of breeding programmes focused on increasing fruit size, relatively little is known about the anatomical and physiological changes required to increase reproductive allocation. To address this gap in knowledge, we compared fruit/ovary anatomy, vascular structure and phloem transport of two varieties of giant pumpkins, and their smaller fruited progenitor under controlled environmental conditions. We also modelled carbon transport into the fruit of competitively grown plants using data collected in the field. There was no evidence that changes in leaf area or photosynthetic capacity impacted fruit size. Instead, giant varieties differed in their ovary morphology and contained more phloem on a cross‐sectional area basis in their petioles and pedicels than the ancestral variety. These results suggest that sink activity is important in determining fruit size and that giant pumpkins have an enhanced capacity to transport carbon. The strong connection observed between carbon fixation, phloem structure and fruit growth in field‐grown plants indicates that breeding for large fruit has led to changes throughout the carbon transport system that could have important implications for how we think about phloem transport velocity and carbon allocation.     

Leishmania in the Chick Embryo. I. Multiplication of Amastigotes of L. donovani in the Liver*

SYNOPSIS. On the 14th day of incubation chick embryos were inoculated intravenously with approximately 4 × 10⁴ amastigotes of Leishmania donovani in ground, infected hamster spleen. Embryos were then incubated at 28, 33, or 37 C. At 1 hr and at 2, 4, and 6 days postinfection embryos were killed, and parasite burdens in the liver and spleen estimated by the method of Stauber. The spleen played a relatively minor role in clearance of amastigotes from the bloodstream and parasites did not survive beyond the 2nd day. In each experiment ～20% of the injected amastigotes were found in the liver after 1 hr. Numbers of amastigotes declined in embryos incubated at 37 C and were not observed later than 2 days postinfection. At 33 C the amastigotes multiplied at a rapid rate, and at 28 C they not only multiplied but, in some instances, transformed to the promastigote form.     

Leishmania in the Chick Embryo. II. Effects of Inoculum Size,Strain Origin,and Stage Injected and Infectivity of Embryo-Derived Parasites for Hamsters*

SYNOPSIS. Amastigotes of Leishmani donovani strains 2S, 3S, 3K, Hm, Gm, and Et were inoculated intravenously into 14-day chick embryos. The course of infection was followed by examinations of liver impression smears. With strain 33 at 33 C incubation, there was a 29-fold increase at 6 days postinfection when the inoculum contained ～4 × 10⁶ amastigotes, but only a ～6.3-fold increase when ～64 × 10⁶ parasites were injected. Infection courses of several geographic strains were compared at 30, 33, and 35 C incubation. Although the results were variable, Sudan strains 2S and 3S appeared to be separate isolations of a single strain. The Burma (Et), Kenya (3K), and Mediterranean (Hm, Gm) strains appeared to be distinct, but confirming evidence of their distinctness should be sought using serologic, epidemiologic, clinical, and biochemical criteria. Strains 2S and 3S multiplied best at 33 C or below, but the embryos usually failed to survive at 28 or 30 C. Multiplication was inhibited partially at 35 C and completely at 37 C. Inoculation of strain 3S promastigotes into chick embryos resulted in a loss of parasites in 1 hr to 2 days postinfection. Only amastigotes were seen in embryos incubated at 28 and 33 C for 4 days. Hamsters infected with parasites passaged once in chick embryos died at median postinoculation times that were closely comparable to those noted among hosts infected with amastigotes from hamster spleen.     

Water relations under root chilling in a sensitive and tolerant tomato species

The shoots of cultivated tomato (Lycopersicon esculentum cv. T5) wilt if their roots are exposed to chilling temperatures of around 5 °C. Under the same treatment, a chilling‐tolerant congener (Lycopersicon hirsutum LA 1778) maintains shoot turgor. To determine the physiological basis of this differential response, the effect of chilling on both excised roots and roots of intact plants in pressure chambers were investigated. In excised roots and intact plants, root hydraulic conductance declined with temperature to nearly twice the extent expected from the temperature dependence of the viscosity of water, but the response was similar in both species. The species differed markedly, however, in stomatal behaviour: in L. hirsutum, stomatal conductance declined as root temperatures were lowered, whereas the stomata of L. esculentum remained open until the roots reached 5 °C, and the plants became flaccid and suffered damage. Grafted plants with the shoots of one genotype and roots of another indicated that the differential stomatal behaviour during root chilling has distinct shoot and root components.     

Water relations of tropical dry forest flowers: pathways for water entry and the role of extracellular polysaccharides

Many trees in tropical dry forests flower during the dry season when evaporative demand is high and soil water levels are low. In this study the factors influencing the water balance of flowers from three species of dry forest trees were examined. Flowers had greater mucilage contents than leaves, high intrinsic and absolute capacitances, long time constants for water exchange and high transfer resistances. Flower water potentials were higher than in leaves and did not fluctuate over the lifespan of the flower. Flower water content also remained constant even though evaporation rates were high, suggesting that water was being supplied from the stem. In two of the species, the water potential gradient between flowers and leaves was opposite to that necessary for water transport from stem to flowers through the xylem, and it was therefore hypothesized that water may enter the flower through the phloem. Calculations showed that nectar production in these flowers could drive a sink of sufficient magnitude to allow water input via the phloem equal to water lost from the flower to the atmosphere.     

EMBRYONIC DEVELOPMENT AND ESTERASE ACTIVITY OF EGGS OF PIERIS BRASSICAE IN RELATION TO TEPP POISONING

The embryological development of eggs of Pieris brassicae was studied in relation to the occurrence of enzymes hydrolysing phenyl acetate and acetylcholine. Phenyl acetate is hydrolysed at a high rate at all stages of development of the embryo. Hydrolysis of acetylcholine only becomes appreciable in the later stages of development. The first significant level of hydrolysis of acetylcholine can be correlated with the development of a nervous system in the embryo to a stage where it may be functional.
Aqueous solutions of TEPP were applied to eggs soon after they were laid. Low doses of TEPP allowed a high percentage of eggs to develop to the point of hatching before death occurred. Most fully developed embryos became active before they died. As the dose was increased less development took place and with very high doses little development occurred.
The significance of these results is discussed. The available evidence does not indicate that the poison penetrates slowly nor that it is 'locked up' and later released. The explanation that seems to fit the evidence best is that the poison penetrates rapidly and reacts irreversibly with, probably phosphorylates, one or more components of the egg, the extent of subsequent development depending upon the proportion of a biochemical system or the number of systems inactivated. Whilst inhibition of cholinesterase may play a part in the poisoning process, at least under some conditions, the evidence indicates that the death of the embryo may result from some other cause.     

Feeding Mechanisms of Babesia equi

SYNOPSIS. Electron microscope and time lapse, phase contrast cinematography studies on Babesia equi organisms within equine red blood cells revealed that this hemoprotozoon has two organelles possibly involved with ingestion of nutrients: a cytostome that takes in hemoglobin from the host cell and a tubule that extends from the main body of the parasite through the erythrocyte to the blood plasma and appears to ingest plasma during periods of rapid growth and development.     

Frequency and Time-Domain Dielectric Measurements of Stem Water Content in the Arborescent Palm, Sabal palmetto

Two methods for monitoring stem water content in the arborescentpalm, Sabal palmetto by determining its dielectric constantwerecompared. The first approach used an oscillating circuit whosefrequency (40 to 70 kHz) was determined by a parallel-platecapacitor that sandwiched a portion of the stem. The secondtechnique was based on measurement of the velocity of an electromagneticpulse (frequency range of 500 kHz and 1 GHz) propagating withina wave-guide embedded in the stem (Time-Domain Reflectometry,TDR). There was basic agreement in the apparent dielectric constantas determined by the two techniques; both resulted in valuesof approximately 90 when the plant was fully hydrated, fallingto values near 50 when water was withheld for one week. The capacitance technique was non-invasive, but was influencedby temperature fluctuations, and we were unable to calibrateit accurately against stem volumetric water content. Insertionof TDR probes did not lead to tissue damage and determinationof an empirical relationship to volumetric water content allowedquantitative estimates of stem water content. Sensitivity ofTDR to small changes in stem water content was restricted bythe fact that attenuation of the pulse within the stem necessitatedthe use of short (0·125 m) wave guides. Despite this,during periods of high transpiration (>10kg plant^–1d^–1) bi-hourly changes in stemmoisture content were detectable. Key words: Dielectric constant, Sabal palmetto, stem capacitance, time-domain reflectometry, water storage