another information about radial water pathway

From: MITSUO SUZUKI <mitsuos@mail.cc.tohoku.ac.jp>
Subject: another information about radial water pathway
Date: Tue, 8 Oct 2002 09:01:27 +0900

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I would like to inform you about a typical radial intercellular space system
which will serve for water conduction.
We presented the following paper on 5th Pacific Regional Wood Anatomy
Conference, Yogyakarta, 2002.

(draft of abstract)
Specialized water-conducting system in roots of a mangrove plant, Sonneratia
alba.

Suzuki, M.12, Sun, Q. 2, Kobayashi, K. 1, Prunbasuki, H. 1 & Suzuki, H. 2
(1: Botanical Garden, Graduate School of Science, Tohoku University, Sendai
980-0862, Miyagi, Japan; 2:Photodynamics Research Center, RIKEN, Sendai
980-0845, Miyagi, Japan)

	Mangrove plants develop highly specialized root system for
adaptation to littoral habitat. Sonneratia alba (Sonneratiaceae) has quite
complicated root system. It radiates メcable rootsモ horizontally in the
ground. The cable roots are anchored by メanchoring rootsモ which are growing
downwards in the soil. Cable roots bear メpneumatophoresモ with a certain
intervals. Pneumatophores grow upwards and finally about uppermost 1/3 of
them are exposed in the air/sea water. From lateral sides of the under 2/3
of the pneumatophores, メfeeding rootsモ come out. Feeding roots run
horizontally and bear many minute roots just look-like as root hairs of
terrestrial plants. In usual, mangrove plants do not have root hair.
	As cable roots and pneumatophores are thick since their origin
(large root apices), it will be expected that they will have no function to
absorbing water. As feeding root has much amount of very fine lateral roots,
it is only candidate that can serve water absorption, while anchoring roots
are medium in size and consequently they may partly function for absorption.
Water absorbed by feeding roots move to trunk via a pneumatophore and a
cable root.
Pneumatophores are extremely specialized roots in morphology and function.
They grow only upwards and never branch. They show conspicuous secondary
growth and form a spindle-like shape. It is generally believed that the
important function of pneumatophores is oxygen aspiration from air and gas
conduction for roots which are developing underground. They have
lenticel-like structure on surface which are exposing in air and aerenchyma
is well developed in cortex. Actually, air conduction is one of the
important functions of pneumatophores, but water conduction is also very
important function of them.
Another important function of pneumatophores is water conduction. Water
absorbed by epidermis of feeding roots enters xylem through endodermis just
same as ordinal terrestrial plants. Water them enter to pneumatophore
secondary xylem. In the secondary xylem, water move horizontally using ray
cells and the intercellular spaces between ray cells. Vessels have lateral
wall pitting facing not only to ray cells (cross-field) but also to the
space. This is the only Sonneratia pneumatophores that have intercellular
space serving for water conduction in ray tissues among all woody plants as
far as we know. As it has fairly specific anatomy in addition to the ray
intercellular spaces, we will introduce more minutely focusing on the
pneumatophore secondary xylem structure in this paper.

Key words: anatomy, mangrove, pneumatophore, root system, Sonneratia alba,
water conduction

After presentation on September 10, we got some arguments from attendants
including Prof. Pieter Baas. The most important problem is  wether the
intercellular space is actually filled by water or by air. We are now
planning further experiments and observations  by employing various methods
including cryo-SEM.


Mitsuo

--------------------------------------
Prof. Mitsuo Suzuki
mitsuos@mail.cc.tohoku.ac.jp
Director, the Tohoku University Museum, Tohoku University
Director, Botanical Garden, Graduate School of Science, Tohoku University
Kawauchi, Aoba, Sendai 980-0862, JAPAN
TEL&FAX(direct) +81-(0)22-217-6788
Office of Botanical Garden TEL +81-(0)22-217-6760 FAX +81-(0)22-217-6766
Secretory (Miss Yagi)  yagi@mail.cc.tohoku.ac.jp  TEL +81-(0)22-217-6761
----------------------------------

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