Evidence for Chromosome Endoreduplication in Eudorina californica, a Colonial Alga

Several nuclear events seen during the cleavage period in Eudorina suggest that chromosome endoreduplication, proportional to the number of cells to be produced, may occur in the gonidia prior to cleavage. Presumably the DNA concentration is reduced to the haploid level during rapid, successive divisions of the cleavage period.
To test this hypothesis, I determined DNA content of gonidia as they grew from 4 μm to 38 μm in diameter between cleavage periods. During growth from 4 μm to 8 μm in diameter, the DNA concentration remained at the haploid level of 0.17 pg/cell. As gonidia in 64 cell colonies continued to grow from 8 μm to 33 μm in diameter, their DNA concentrations increased 60-fold.
Analysis of the Eudorina DNA by equilibrium centrifugation in CsCl showed only 2 bands with buoyant densities of 1.721 g/cm³ and 1.699 g/cm³, presumed to be nuclear and chloroplast, respectively, on the basis of labelling with ³H-thymidine and ³H-adenine. The 8: 2 ratio of the two bands did not change with increase in cell size and no other bands were detected, suggesting that both nuclear and chloroplast DNAs were synthesised proportionately prior to the cleavage period.     

Enhancement of Gibberellic Acid-stimulated Hypocotyl Elongation of Lettuce (Lactuca sativa L. cv. Grand Rapids) by Phlorizin and Light

The interaction of light, gibberellic acid (GA₃), and phlorizinin the growth of lettuce (Lactuca sativa L. cv. ‘GrandRapids’) hypocotyls was investigated. At all concentrationsof GA₃, phlorizin enhanced GA₃-induced growth at luminous intensitiesabove 50 ft-c (continuous light). Without GA₃, phlorizin hadno effect on hypocotyl growth in the light but it inhibitedgrowth in the dark. Both seedlings and hypocotyl sections respondedto phlorizin in the presence of GA₃. There was no iteractionbetween phlorizin and KCl. Water-growth was severly inhibitedby light. GA₃,-induced growth was slightly inhibited by light,and then only at luminous intensities above 50 ft-c. Thus, relativeto H₂O-growth, GA₃-induced growth increased with increasingluminous intensity up to 450 ft-c, where it reached saturation.It seems that a synergism may exist between light and GA₃ aswell as between phlorizin and GA₃. Lactuca sativa L, lettuce, hypocotyl elongation, gibberellic acid, phlorizin, light