Early Effects of Excess Boron on Photosynthesis and Growth of Cucurbita pepo

Summer squash plants {Cucurbita pepo L., cv. ‘Early ProlificStraightneck’) hydroponically cultured under optimal boronnutrition (+ B)³ until age 5 d were transferred to hydroponicsolutions supplemented with excess boron (+ + B)³. As boronaccumulated in the leaves with time, leaf conductance to watervapour, ¹⁴CO₂ fixation, and chlorophyll content of the oldestleaf became significantly less than in the + B-control plantsof the same age; shoot growth essentially ceased. Boron alsoaccumulated in the roots; concomitant inhibition of root elongationand lateral root development resulted. These metabolic changesall occurred prior to the accumulation of sufficient boron tocause the appearance of any symptoms characteristic of borontoxicity. Key words: Boron toxicity, Stomatal conductance, Photosynthesis, Transpiration, Shoot and root growth, Cucurbita pepo     

Salt Stress Causes Acceleration of Purine Catabolism and Inhibition of Pyrimidine Salvage in Zea mays Root Tips

Nucleotide metabolism was studied in apical 5.0 mm root tipsof corn plants (Zea mays L., cv. Pioneer 3906) hydroponicallycultured for 7 d and then salinized for 19 d at a rate calculatedto reduce the osmotic potential (_o) of the solutions by O.1MPad^–1 to a final _o = -0.4 MPa. Saline treatments withtwo different molar ratios of Ca₂₊/Na⁺ were employed, viz.,0–03 (2.5 mol m^–3 CaCl₂ + 86.5 mol m^–3 NaCl)for the NaCl treatment and 0.73 (31.5 mol m^–3 CaCl₂ +43.1 mol m^–3 NaCl) for the NaCl + CaCl₂ treatment. Bothsalt treatments reduced root growth by more than 30%. The capacityof roots to provide purine nucleotides either by de novo synthesisor by re-utilization of existing bases, e.g. salvage of hypoxanthineto adenine nucleotides, was not affected by either salt treatment.However, catabolism of hypoxanthine was accelerated more than3.5-fold by both salt treatments, demonstrating an increasedcapacity for purine catabolism which would shift the normal1: 1 ratio of synthesis: degradation of purine nucleotides observedfor the roots of healthy control plants to less than 0.2 duringsalt stress. The ratio of pyrimidine nucleotide synthesis: degradationwas also reduced. In this case, the unfavourable shift towardnucleotide degradation resulted because both salt treatmentsreduced salvage capacity by more than 25%, but had no compensatingeffect on de novo synthesis or catabolism of pyrimidines. Key words: Salinity, osmotic potential, nucleotide metabolism     

The impact of population bottlenecks on fluctuating asymmetry and morphological variance in two separate populations of reindeer on the island of South Georgia

In the early part of the 20^th century, whalers on South Georgia in the South Atlantic transported reindeer from Norway to establish a population from which they could cull animals for food. This happened twice, with reindeer obtained from the same source in each case, and with independent founder populations being established on separate parts of the island. As the exact number of founding males and females are known in each case, and as it was possible to obtain materials from the source population, this provided an unusually clear test of expectations about the impact of population bottlenecks on morphological and genetic diversity. In this study, we focus on the impact on morphological variation and on the relationship between genomic stress and indirect measures of fitness. We find that fluctuating asymmetry and morphological variation increased in each bottlenecked population and that the impact was somewhat stronger for the founder group that began with fewer females. Based on several skull measurements, there was also a significant trend for the reindeer in the bottlenecked populations to have smaller skulls. There were consistent correlations between individual genetic diversity and indirect measures of fitness, but these were weak and non‐significant after correction for type 1 error. Taken together, these data support the expectation that genomic stress has the potential to impact the expression of morphological phenotype in a large mammal and provide an opportunity to directly compare two parallel events. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 798–811.     

Relationship between the activity of the orotic acid pathway and glucose content of roots of Cucurbita pepo

Abstract. Apical 3-cm root segments excised from 2-d-old squash seedlings ( Cucurbita pepo L. cv. Early Prolific Straightneck) that were germinated and grown between sheets of paper towelling moistened with H₂O₂ incorporated 144±10 nmol (± SE. n = 15) NaH¹⁴CO₃ into uridine nucleotides (∑UMP) per gram intact roots during the 3-h incubation period ( Lovatt, Albert & Tremblay, 1979 ). Continued culture of squash seedlings in this manner for an additional 24 or 48 h had no effect or slightly increased (30%) the activity of the orotic acid pathway. However, transfer of 2-d-old seedlings to Shive's nutrient solution reduced the activity of the orotic acid pathway within 15 h to 2.3 nmol NaH¹⁴CO₃ incorporated into ∑UMP per gram apical 3-cm root segments during the 3-h incubation period. The observed decrease in capacity to synthesize pyrimidine nuclotides de novo paralleled the reduction in glucose content of the roots and was reversed by supplying glucose during hydroponic culture in Shive's nutrient solution. Root elongation was not affected by the reduced activity of the orotic acid pathway nor by the decreased level of available glucose.