Abstracts of Papers - Harvard Forest - Harvard University

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PETERSON, CURT M.* and MICHAEL W. FOLSOM. Depart- ment of Botany, Plant Pathology, and Microbiology and the Alabama Agricultural Experiment Station, Auburn University, AL 36849, and Department of Botany, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. - The effect of a cytokinin on flower and pod abscission of soybean, Glycine max (L.) Merr. Abscission of flowers and immature pods accounts for most of the reduction in yield potential of soybean (Glycine max (L.) Merr). Terminal racemes of 'Bragg' soybean plants were sprayed with 10-, 10- or 10-3M 6-benzylaminopurine (BAP) to determine the influence of a cytokinin on flower and pod abscissior. A significant reduction in abscission occurred only when 10-3M BAP was applied. A significant increase in the total number of seeds per plant also was observed for the 103M BAP treatment. This was due entirely to an increased number of pods per raceme, because there was no difference in the mean number of seeds per pod. Most abscissions within each treatment occurred during the first 14 days of the treatment period. The effect of BAP in reducing abscission was observable within 10 days after spray- ing. All mature pods of control plants were located at the first seven (proximal) nodes on terminal racemes. Compared to other treatments the increased number of mature pods following 10-3M BAP treatment was due to a significantly higher number of mature pods at nodes distal to node 7. Changes in distal shoot morphology were observed on some treated plants suggesting that BAP may alter reproductive development to favor increased pod set in soybean. PnT'nOLY TOTIN J.* "Tew York Botanircal '-rden, IBronx, NY 1fl453 nnrv ~),.'TIS 'Nf, STEJx7ENSO'\J, larnarr1 Coi1ee of Colurmibira TTnive.rqi.tv, 'TY 1(),)27. - PhvllotAxis, ste?nr mornTol1oov and shoot ani.cal organization rof T.v conodtlimt annre.s sum (TL.vcnodiaceae) . ThvI-otnxis consists or i svste.n of alternatino nsendowhorls cCOrre-sPnQs witeh a 2/1 Ti-ivIlotactic tn a o+O contact nar.atiai sn-tral whlrch system wr.th 13 orthlosti.chlos. Eachi of the six stelar lobehs is svm.poliun of the. leaf tracps oF thlree nrtqosticlilns afld i.5 eenn of th~ree nrot.oxvlern noles. ANt th-e verv lenst, the otitt,.r reginn of t'sA. stele is CoTnroqed of leaf traces and is t'verefore not corinleteiv mtitonomous. The. s'rnotc an?x con.si.sts of Sotxr zones3 whiich mav he rpcnf 7:lr4 both cvtolo"icn1llv an.d h-iistr,chp?irn.v, as foliow7s: suirface initials, subizilrface in1ti.i1 , rii1 r'ier1stern, ond ne.riphrwta.l rneristemn. The c{.ff freni
30 Developmental and Structural Section REYNOLDS, THOMAS L. Department of Biology, University of North Carolina, Charlotte, NC 28223. - An ultrastructural and stereological analysis of pollen grains of Hyoscyamus niger during induced embryogenic development. Selected nuclear and cytoplasmic changes during embryogenic development, induced by the culture of anther segments of H. niger, were analyzed using stereological techniques for morphometry. When pollen grains were cultured at the uninucleate stage of development, potentially embryogenic grains could be identified within 6 h of culture by an increased area fraction of the nucleolus occupied by the granular zone. The ratio of dispersed to condensed chromatin in the nucleoplasm of these cells also increased. Nonembryogenic pollen in vitro and in vivo possessed prominent fibrillar zones in the nucleolus and a relatively constant ratio of dispersed to condensed chromatin. These differences may reflect changes in nuclear activity in potentially embryogenic pollen grains during early stages of culture. Following the first haploid mitosis, the nucleolus of the generative cell in potentially embryogenic pollen maintained an extensive granular zone through the first division to form a proembryoid. On the other hand, the nucleolus of the vegetative cell became primarily fibrillar and the cell did not divide. The area fraction of the cytoplasm occupied by RER, Golgi cisternae, mitochondria, and plastids differed in the generative cells of potentially embryogenic and nonembryogenic pollen. These results support the idea that embryogenic induction in H. niger takes place at the uninucleate stage of pollen development and that the first division of the potentially embryogenic generative cell to form a bicellular proembryoid completes the induction process. Richards, J.H. and S.C.H. Barrett. Dept. of Biol., Fla. International U., Miami, FL 33199 and Botany Dept., U. of Toronto, Tor- onto, Ontario, M5S lAl. Developmental basis of tristyly in Eichhornia paniculata Spreng. (Pontederiaceae). Eichhornia paniculata is a short-lived per- ennial, emergent aquatic. The species is tristylous but self-compatible. Growth is sympodial. When flowering, paniculate in- florescences bear flowers alternately on first-order branches. Long, mid and short- styled morphs occur in the majority of Braz- ilian populations. A flower of a given morph has a style of one length and six stamens, three each of the other two lengths. Stamen insertion is dorsiventral. Within a flower, the relatively longer stamens are found on the lower side of the flower, while the relatively shorter stamens are on the upper side. Anther size is positively correlated with stamen height. The general pattern of flower development does not differ between morphs. Flower prim- ordia are triangular at initiation. Stamens arise in two whorls of three each in conjunc- tion with tepal origin on the flat primordium apex. The three horseshoe-shaped carpel pri- mordia arise simultaneously after the second set of stamens. Thus, initial organization of the flower is radial. Differences between the two stamen levels in size and number of microsporocytes are seen in anthers prior to meiosis. Meiosis occurs in buds app. 1 mm long. Thus the dorsiventral pattern of development first seen in the microsporocytes alters the initial radial pattern of growth. RIDING, RICHARD T. Department of Biology, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 6E1. -Structure of needles of Pinus radiata as influ- enced by light intensity or moisture stress. Trees from four clones were grown in growth rooms at the New Zealand Forest Service, Forest Research Institute in Rotorua. Current year needles, collected from different heights in the crowns of these trees, yielded foliage samples from four light intensities per clone. Needle size increased with increasing light intensity. This was accom- panied by an increase in the number of hypodermal layers, mesophyll layers, and resin ducts. The ratio of vascular tissue to needle cross-sectional area remained fairly constant; however, the dis- creteness of the two vascular bundles decreased as stelar size increased. Although the 'structure of epidermal cells and the stomatal complex did not vary with light intensity, the number of stomatal rows and stomatal frequency tended to increase with increasing light intensity. The influence of vapour pressure deficit (VPD) on needle structure was determined for plants from 3 clones grown under 3 different conditions of atmospheric moisture. The needles with the smallest cross-sectional area were from dry conditions while the thickness of the dermal system was greatest for plants grown under moist conditions. The number of resin ducts per needle increased with decreas- ing VPD. Again, the structure of the stomatal complex was constant for all conditions. In both studies there was clonal variation. (Supported by grants from NSERC Canada. Thanks are due D.R. Smith and D.A. Rook of the Forest Research Institute.) ROST, THOMAS L., PRIMAVERA IZAGUIRRE DE ARTUCIO* AND EDWARD B. RISLEY. Department of Botany, Uni- versity of California, Davis, CA 95616; *Facultad de Agronomia, Universidad de la Republica Uruguay, Montevideo, Uruguay - Transfer cells in the placental pad and caryopsis coat of Pappophorum subbulbosum Arech. (Poaceae). During caryopsis development the layers of the pericarp, integuments and nucellus all contribute to the formation of the caryopsis covering structures. The caryopsis coat is continuous around the entire caryopsis except at the style remnant and placental con- nection. The coat consists of a discontinuous outer pericarp epidermis transfer cell layer, crushed and senescent middle pericarp layers and a continuous inner pericarp epidermal transfer cell layer. This last layer, however, is not present across the placental pad. The integuments are present as a crushed dense layer, the nucellus is a discontinuous, thin and crushed layer. The placental pad occurs at the ventral surface of the caryopsis opposite the scutel- lum and coleorhiza. It consists of 15-20 crushed cell layers, including the remnant of the placental vascular bundle. From the inside several partially crushed nucellar layers occur that contain transfer cell walls. The middle dense layers, the pigment strand, consist of the middle pericarp remnant, plus the placental vascular bundle remains. The inner pericarp epidermis and aleurone layers do not extend across the pad. The outer pericarp epidermis extends across the entire pad as a connected layer of transfer cells. These cells contain membranous structures suggesting that they may be living cells, possibly functional in the mature caryopsis.
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