Mo megaspore megagametophyte endosporic archegonium

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Unformatted text preview: maining one develops into a female gametophyte within the megasporangium (nucellus)   Female gametophytes produce eggs within archegonia micropyle Integument Megasporangium (nucellus) Megasporocyte (2n) Pine life cycle   Alterna�on of genera�ons (diploid/haploid)   Life cycle span 2 years (pine) ♂ Spring, yr1 Megaspores (n) ♀ 6-12 mo Megaspore Megagametophyte (endosporic) Archegonium with egg Pollina�on The pollen grains are released from the sporophyte and transferred to the vicinity of the egg   Wind   Outcrossing   Large amounts of pollen yr2 (15 mo) Autumn, yr2 Pine life cycle: pollina�on   Two wing-­‐like structures on the pollen grain aid the pollen to be carried by wind   The male gametophyte 4-­‐celled: genera�ve cell and tube cell (and 2 prothallial cells)   The genera�ve cell divides to produce two sperm cells   The tube cell grows toward the egg, producing a pollen tube 8 Pine life cycle: fer�liza�on   Sperm transferred directly through the pollen tube to the egg   The two sperm cells are released and move toward the egg   Eggs in archegonia   One sperm nucleus unites with the egg nucleus (the other degenerates)   Sperm non-­‐mo�le (water is not required for reproduc�on) Other gymnosperms: Cycads   Palm-­‐like plants, but true secondary growth   Mainly tropical-­‐subtropical (Zamia pumila na�ve to Florida)   Plants are dioecious (seed cones and pollen cones)   Mul�flagellated sperm   Specialized pollina�on (insects)   Harbor cyanobacteria (nitrogen fixa�on)   O�en highly toxic (but starch used as food) Pine life cycle: seed development   Zygote develops into a suspensor and proembryo (polyembryony – only one survives)   Seed: – Integuments (and remnants of nucellus) develop into seed coat – Gametophyte (food reserve) – Embryo: root-­‐shoot axes, cotyledons (several)   Cones mature and seeds are dispersed   The seed is the dispersal unit! scale seeds Other gymnosperms: Gingko   Only 1 species, Gingko biloba (China)   “Living fossil” (270 my) -­‐ no na�ve popula�ons?   Important cul�var, tolerate pollu�on   Short shoots/long shoots   Unique fan-­‐shaped leaves, deciduous   Dioecious (no cones)   Mul�flagellated sperm   Fleshy coated seeds (smelly!)   Medicinal uses 9 Other gymnosperms: Gnetophytes   Monophyle�c but diverse group   Gnetum: trees and vines with leathery Introduc�on to...
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