STUDIES ON RESPIRATION IN DEVELOPING POPPY SEEDS

The excised ovules of Papaver somniferum have been used to investigatethe endogenous uptake of oxygen during their maturation intoseeds. Effect of some activators and inhibitors and the activityof succinic dehydrogenase have been studied. There appears tobe an intimate correlation between respiration and the anatomicalchanges in the ovule. There is an increased oxygen uptake duringor immediately preceding the events of (a) pollination, (b)divisions of the endosperm nuclei, (c) cell wall formation inthe endosperm, and (d) elongation of cotyledons. The activityof succinic dehydrogenase follows a curve essentially similarto that of oxygen uptake. The low intensity of respiration duringcertain period of development appears not to be due to exhaustionof endogenous substrates. Endogenous substrates do, however,appear to be limiting on the days when maximum respiration occurssince added sugar does significantly enhance oxygen uptake.The results with two inhibitors, iodoacetate and fluoroacetate,suggest the operation of glycolysis and tricarboxylic acid cycleduring the earlier phase of seed development when the rate ofgrowth is highest. (Received September 1, 1964; )     

Haustorial Role of Pollen Tubes

In angiosperms, the pollen tube is siphonogamous and its mainfunction is to carry the male gametes for double fertilization.In some taxa, as in Cucurbitaceae, the tube branches after enteringthe ovule, prior to fertilization. The tube may even swell andform a bulla. During post-fertilization development of the ovule,a portion of the tube may persist in the micropyle, or in theembryo sac, or in both, sometimes even in the micropyle of themature seed. Haustorial function has been presumed in a numberof taxa. In Grevillea, following fertilization, the pollen tube branchesat the micropyle, and the branches grow intercellularly intothe ovarian tissue where further branching occurs. A haustorialrole of the pollen tube is presumed from circumstantial evidence.In gymnosperms (for example, Cycas, Zamia and Ginkgo) the pollentube is nonsiphonogamous, arises from the distal (upper) poleof pollen grain, and grows laterally in the apical region ofthe nucellus. The tube branches in Cycas and Ginkgo but remainsunbranched in Zamia. These pollen tube branches are enucleate,and are not concerned with the transport of male gametes forfertilization. However, the haustorial role has been well documented.In Podocarpus, the pollen tube is siphonogamous and arises fromthe proximal (lower) pole of pollen grain. After traversingthe nucellus, the tube forms a bulla at the point of contactwith the female gametophyte, and several branches originatefrom the bulla. The pollen tube branches grow along the innersurface of the nucellus and the outer surface of the femalegametophyte. The haustorial role of the pollen tube branchesis uncertain. Procedures for convincingly demonstrating thehaustorial role of pollen tubes are discussed. Angiosperms, gymnosperms, pollen tube, bulla, fertilization, haustorial role     

CHANGES IN THE CARBOHYDRATES, PROTEINS AND NUCLEIC ACIDS DURING SEED DEVELOPMENT IN OPIUM POPPY

This investigation is concerned with the major changes in thelevels of carbohydrates, proteins, nucleic acids and some enzymesin the ovules of Papaver somniferum at various stages of seeddevelopment. Of the soluble sugars, fructose and glucose arepresent in large amounts up to the free nuclear stage of theendosperm but decrease rapidly when the latter turns cellular;then sucrose becomes most abundant. At this time the concentrationof insoluble carbohydrates is almost one-seventh that of solubleand the activities of - and ß-amylases are at theirhighest. The nitrogen in the seed is accumulated in two phases,the first coinciding with the development of endosperm and thesecond with the development of embryo. Cell wall formation inthe coenocytic endosperm is accompanied with a marked decreasein the soluble nitrogen. The activity of glutamic-alanine transaminaseincreases concurrently with the increase of protein in the ovules.The maximal RNA content is attained after the ovules have completedtheir increase in size but prior to the deposition of proteinaceousreserves in the endosperm. The amount of DNA increases withthe growth of endosperm but decreases during the maturationof embryo. Both ribonuclease and deoxyribonuclease show twopH optima corresponding to pH 5.5 and 7.5 (ribonuclease) and5.0 and 7.5 (deoxyribonuclease). Their activities seem to becorrelated to the levels of nucleic acids. ¹ Present address: AEC Plant Research Laboratory, Michigan StateUniversity, East Lansing, Mich., U.S.A.     

GROWTH, DEVELOPMENT AND RESPIRATION IN THE OVULES OF ZEPHYRANTHES LANCASTERI AT DIFFERENT STAGES OF MATURATION

Changes in the rate of respiration and activity of succinicdehydrogenase in the ovules, embryo and endosperm have beeninvestigated at different stages of seed development in Z. lancasteri.An attempt has been made to find any possible relation betweenphysiological changes and the growth pattern of ovule. The fertilizedovules mature into seeds in 16–19 days from the time ofpollination. The respiratory course and the growth of ovulesfollow identical trends. The curve for oxygen uptake is characterizedby at least two peaks; the first on the sixth or seventh dayis related to the laying down of walls in the coenocytic micropylarchamber of the endosperm and the second on the 11th day precedesthe elongation of cotyledon. In excised endosperm the activityof succinic dehydrogenase is highest during its transformationfrom freenuclear to cellular state, while in the embryo it isso after the attainment of mature size. ¹Present address: AEC Plant Research Laboratory, Michigan StateUniversity, East Lansing, Mich., U.S.A.     

CHANGES IN THE CARBOHYDRATES, PROTEINS AND NUCLEIC ACIDS IN THE OVULES OF ZEPHYRANTHES LANCASTERI AT DIFFERENT STAGES OF MATURATION

The major changes in the levels of soluble and insoluble carbohydrates,nitrogenous compounds and nucleic acids were investigated atdifferent stages of seed development in Zephyranthes lancasteri.The activities of amylases, glutamic-alanine transaminase, ribonucleaseand deoxyribonuclease were also studied. The alcohol-solublenitrogen and carbohydrates attain their maximal levels priorto the elongation ofthe cotyledon. Both of these decrease markedlyduring further maturation of the seed. The accumulation of totalnitrogen in the ovule follows a sigmoid pattern. The glutamic-alaninetransaminase activity appears to be exclusively localized inthe endosperm and is absent from the embryo. The embryo seemsto derive its organic nitrogen fromthe endosperm. The peak inthe level of DNA per ovule is attainedprior to the elongationof the cotyledon while that of RNA is foundsoon after. ¹Present address: AEC Plant Research Laboratory, Michigan StateUniversity, East Lansing, Mich., U.S.A.